It was Saturday afternoon, exactly one week before the Easter holidays were scheduled to begin. This year, Easter fell at the end of March, and the holidays always surrounded the week before and the week after the Christian holiday. Harry was looking forward to them. There wouldn't be a feast, but they would have two interrupted weeks together, as most of the students staying behind would be preoccupied with homework and studying for end-of-term exams.

Harry's dad looked up from his meal, and spoke softly. "Harry, would you like to go to beach during a part of our summer holidays?"

The question caught him off guard, so much so that he nearly dropped his half-eaten sandwich. His dad smiled in amusement as Harry looked at it like he wasn't sure it was truly there, then took a bite. He needed the time to think. The Dursleys had gone to the beach several times, always for at least a week. Harry hadn't been allowed to go, of course. Mrs. Figgs had been in charge of his care. While he hadn't enjoyed spending afternoons at her house, he hadn't minded these longer trips as much. Her cooking wasn't as good as his Aunt Petunia's, which had been a shame, because he'd been allowed to eat larger portions. Her house contained a spare bedroom, and Harry had gotten quite used to sleeping in a proper bed, with two warm blankets.

Dudley would always go on and on about how much fun they'd had. How they would spend hours lazing on the beach, and eat lots of delicious food. Aunt Petunia would say that she needed to lose weight afterwards, because of how much she'd eaten. But Uncle Vernon would just laugh and kiss her.

Harry knew that he wouldn't have had any fun if he had gone. Dudley would probably have tried to bury him in the sand, or force his head under the salty water. Staying with Mrs. Figgs was never fun, not like the fun times Dudley had, but it was safer.

Still. Now that Harry was living with his dad, a part of him very much wanted to go on a beach holiday with his new dad. But there was a problem. A very big problem.

He'd never learnt to swim.

It wasn't something he'd hid from his new dad, as much as it had simply never come up before.

"I-I don't know how to swim, Dad," he admitted.

"I can see how this would be an impediment to a beach holiday," Severus said, with a nod.

Oh. Then, they wouldn't go. Harry tried not to feel too disappointed.

Then, Severus stood, and came around to Harry's side. Bending so they were at eye level, he placed his hands on Harry's shoulders. "Would you like me to teach you to swim, owlet?"

Harry felt his eyes widen. "Really?" Then, a thought occurred to him. "But, er, it very difficult to learn?"

It couldn't be terribly so, as Dudley had learned, after all. Aunt Petunia and Uncle Vernon had made sure he'd taken lessons, and they'd insisted he take it seriously.

"If you don't know how to swim, son, you're always in risk of drowning," Uncle Vernon had told him. Then, he'd glared at Harry, sending the message clearly: "We don't care if you drown."

"It can be," Severus allowed, "but I'll teach you slowly." Severus squeezed Harry's shoulders. "We'll begin next Saturday, at the start of the Easter holidays."

A week later, they walked to the lake, a place where students often gathered, but--like the Forbidden Forest--was off limits to Harry without his dad present. Severus had ordered special robes for Harry, which he called, "swim robes." They were green, shorter than his usual robes, as they reached only a little below his knees. The sleeves, too, ended at his elbows. The material was very thin, rather light the night shirts Harry had worn in August. His dad had a matching set, only they were-of course-in black. Harry's were dark green in color.

It was chilly enough that their cloaks needed Heating Charms. Harry wondered how they'd manage the water, which couldn't be very warm at this time of year. Dora had told Harry that most students didn't bother swimming in it until nearly the end of term. Severus carried a bag which looked small, but Harry knew it contained an Extension Charm. Inside were two giant towels, and two plastic bags. The first one contained two chocolate frogs, but the second was filled with what looked like rat tails. Severus opened that bag first, then divided the contents into two. He handed half to Harry, who took it with reluctance. It felt slimy in his hands.

"It's called gillyweed," Severus explained, before Harry could ask. "It's a plant that allows you to breathe underwater for ninety minutes. That is, it allows an adult to breathe underwater for that long. Children might be able to remain longer, but that's not something I wish to experiment with on your end, owlet."

Harry studied it. "Do I hold it to my nose, then, to be able to breathe?"

Severus chuckled. "No, not like that. You eat it, child. The plant provides a rather partial transfiguration on your body-just temporarily, of course. It gives you gills, which allow you to breathe like a fish or aquatic creature. As I'll begin teaching you how to swim, it's necessary for you to have the option of being able to breathe under water." He paused. "Once you swallow it, you will need to immerse yourself fully in the water, as you won't be able to breathe the air."

Harry nearly dropped the plant. "I don't want to! Not if I can't breathe above water, Dad!"

His dad drew him close. "Very well, we'll take a different approach." Severus thought for a moment. "I'll charm our robes to heat us up. Perhaps, we'll try the Bubble Head Charm, much later, to allow you to breathe underwater," he added, smiling.

"Thank you," Harry murmured.

He tousled his hair. "You're welcome. Well, hand the plant back back, then."

"Okay."

Severus returned the plant to the bag, then removed his cloak, nodding for Harry to do the same. When he pointed his wand at Harry's swim robes, the sudden chill was replaced by a very powerful warmth. His guardian pointed his wand at himself, and a moment later, his expression similarly softened.

They walked into the shallow part of the lake, which was initially freezing, but the heat from Harry's robes made it bearable. Dora had said that students only swam in the lake near the end of term, and not very far out. Far underneath, she'd explained, lived creatures that were not exactly dark, but not pleasant to encounter.

"They leave us alone at the surface," Dora had reassured Harry. "We joke about the Giant Squid eating Sl-some mean students, but it's never happened."

Harry felt further reassured by the secure knowledge that his dad wouldn't put him in harm's way.

"Let's stop here," he said, interrupting Harry's thoughts. "That is, we shall go no deeper for the time being."

The water, Harry saw, was somewhere between his waist and his shoulders. On his guardian, it was below his waist. It still felt rather chilly, but not unbearable.

"Okay," Harry answered, staying close to his dad.

"Are you cold? Do you wish me to increase the charm?" Severus asked, wrapping Harry in a hug.

"It's a bit chilly, but it's not too bad," Harry said, truthfully.

"Very well. If it becomes too cold, do tell me. I can either heighten the charm, or we can end your swim lesson early," Severus replied, smiling. "Now, today, we'll start with the basics. I want to show you how to kick. Not to kick me," he said, quickly, laughing. "Here. Grab hold of my shoulders..."

Harry gripped onto the older man's shoulders, not wishing to hurt him, but also not wanting to let his hands fall.

"Good. Now, see how your legs are in the water?" Severus asked, calmly.

"I think so..." He could feel them, of course, and the water soaking his robes through. But he couldn't see them...

"Yes, you're doing fine. Now, owlet, slowly kick them. Don't let them attack the water, mind, just move them back and forth. Good," he praised, as Harry obeyed. "We'll do this a bit longer..."

Harry felt his legs growing a bit tired when his dad gave his next instruction. "Very good, Harry. Now, I'll move in the water, and you continue to kick."

It wasn't exactly more difficult to do this, but it was a bit unsettling all the same. Harry could feel his dad moving around, and latched his hands more tightly onto his robes. Chewing on his lips in concentration, Harry continued to kick as his dad moved, the water not growing any deeper along his frame. Finally, Severus set Harry down. The feel of solid ground against his feet felt wonderful.

"Tired?" he asked, wrapping both arms around Harry.

"A bit," Harry admitted, snuggling close to his dad. The water didn't feel cold anymore, but his dad was nice and warm. Finally, though he let go.

Severus smoothed back his hair. "One last lesson today, if you're not too tired. It's rather more enjoyable than kicking, and less physical energy."

"Yeah?" Harry asked, looking up.

"Indeed." His dad grinned. "Blowing bubbles."

That was quite fun! It was easy, too. Harry had only to take a deep breath, and blow out with his mouth under the water. The bubbles flowed in a trail, the first ones popping before Harry managed the last, but it made him smile in between breaths.

Like the kicking, though, it got rather tiring after awhile. Harry didn't exactly feel like he would fall asleep in the water, but he did hope the lesson would be over soon.

His dad seemed to be able to read his mind. "I expect that's enough for today," he said, lifting Harry in his arms. "You'll have a nice bath, and perhaps a good, long rest afterwards."

Harry let himself slump against his dad's shoulders. "Thank you for teaching me how to kick and blow bubbles."

"You're welcome. We'll have the next lesson in a day or so." Added warmth filled Harry, and then, his dad lowered him to the ground. He wrapped a towel around him, which must have contained a Heating Charm, because further warmth filled Harry from head to toe.

He felt awake enough to manage a bath on his own, especially since the shampoo suds couldn't get into his eyes and burn them. Severus filled up the tub, adding a bubble bath mixture, and after kissing Harry on the top of his head, left him to it. Harry stripped himself of the huge towel and his swim robes, both of which were now quite wet, and made himself comfortable in the hot water. He relaxed for some time, just enjoying the warmth. As good as the Heating Charm had been to keep him from freezing, the lake water had been chilly, and seemed to cling to his robes. This water took away all of the coldness.

The shampoo, too, worked extra hard on his hair. Severus had explained that while it always gave your head a good massage, it worked harder if your hair was less than clean. Harry had washed his hair last the day before last, but the lake water must have made it dirtier than usual. On and on, the massage went, from the top of his head to the bottom of his neck. Only his dad could have done as well. Then, it was all he could do to stay awake long enough to rinse all the suds away, and wrap himself in a warm towel.

Harry debated between robes and a night shirt. It was the middle of the afternoon, but he'd already had his bath for the day. He settled on a night shirt, deciding that even if his dad told him to change, he wouldn't yell at him.

To his surprise, his guardian was similarly dressed, and chuckled when he saw Harry.

"I expect that we'll be dressing for bed rather earlier than usual," he remarked, reaching out his arms for a hug. "What did you think of your first swimming lesson?"

Harry nestled against his dad's warm frame before answering.

"It was hard work, but I liked it. Especially learning how to make bubbles!" he added, laughing.

Severus chuckled, giving his arm a light squeeze. "A most enjoyable pastime. Are you hungry?"

But Harry shook his head. "A bit tired."

Then, a long yawn exploded from him.

"More than a bit, I expect," Severus lightly chided. "Very well. We could both use a rest. My bedroom, yours, or the couch?"

"Can we have a fire here?" Harry asked, hopefully.

"Certainly." He flicked his wand, and a large, warm fire appeared.

Then, Severus lifted Harry into his arms, and guided them both onto the couch. Harry felt it expand underneath him, and then the warmth of blanket with Heating Charms wrapped snugly around his entire body. Only his head was exposed, and the cushions of the couch felt soft against it. Harry sighed happily.

Harry learned against his dad's chest, listening to his steady heartbeat. Harry felt as though his insides were as warm as his body. Severus pulled him a bit closer, then adjusted his head slightly, and then, to Harry's delight, began to run his hands Harry's damp hair. He felt himself relax fully into the touch, his eyes close on their own.

"I love you, Dad," he murmured.

"I love you too, sweet child," Severus answered, his voice soft, but filled with warmth. "Sleep well."

"You too, Daddy," Harry yawned.

He slept soundly, dreaming of swimming in an ocean he had yet to visit.

They returned to the lake the following day, each wearing their swimming robes. Harry was glad when his dad did not bring up Gillyweed again, just warmed their robes with his wand. As they made their way into the cold water, Harry thought his dad was lucky to be able to do magic like that. His own magic was still accidental at this point, and he wouldn't be given a wand until a little before he started as a student. Over two years remained.

His dad interrupted his thoughts. "You did well yesterday, Harry, and we'll simply review kicking and blowing bubbles before I teach you how to use your arms in the water. Then, I believe, I shall hold you in the water, and you can put the two movements together. I will not let you go," he added, as though reading his mind. "Not for some time, or until you're ready."

"What if I sink?" Harry asked, suddenly fearful.

"Then, I shall scoop you up," Severus promised. "But I don't believe you shall, and besides, that's still a ways off."

So Harry nodded, reassured, and they began their second swimming lesson.

In many ways, it was easier to make the arm movements than the leg ones. He needed only to put his arms in the water and then out, rather in a circular motion. It still got a bit tiring over time, but his dad seemed pleased with his progress.

"It's the water that makes it more difficult, just like you walk slower in the water than on land," Severus explained. "If you were to walk a mile, it would only take twenty or so minutes. Swimming that length would be a far more lengthy process, and you would be exhausted by the end. As would I, I expect, though I never attempted it."

"Do many of our kind?" Harry wondered.

But Severus shook his head. "Unlike Muggles, we have but one sport. After you see a Quidditch game, I expect watching people swim would be quite dull."

Harry grinned. "I reckon so!"

The next part, which took place the following day, was far more difficult. After they ran through the exercises, Severus lifted Harry so his body was at the surface of the water. But even though his hands were firm on his stomach, keeping him upright, Harry panicked immediately.

"I can't-Daddy, I can't! Please put me down!" he nearly screamed, grabbing at his dad's hands.

His dad did not delay. As soon as his feet were firmly on the ground, Harry felt a bit better, but also ashamed and no less afraid of what could have happened.

"Harry." His dad turned and faced him, lowering himself in the water so they were at eye level. "What happened, child?"

He began to cry. "I felt like I was going to fall."

"Shh, shh, it's all right." His guardian drew him close, holding him tightly against him. "You're safe. I won't let anything happen to you."

Harry just buried himself in his dad's robes, clinging to him as tightly as he could. His guardian let go of one hand for a moment, but it was only to make small circles along Harry's back. Not that he could feel it very much, not the way he could when he was in his night shirt and had experienced a nightmare. But he was still aware of the hand on his back, and the other holding him close.

After he'd calmed enough to let go, his dad put a hand on his shoulder, and spoke softly.

"Can you express what made it so uncomfortable? Was it being immersed in the water, or something else?" Severus asked, gently.

Harry knew the answer, but wasn't sure if he could explain it clearly. "When I practiced kicking, I knew I could hold to your shoulders. And when I learned how to move my arms, I had my feet on the ground. But being in the water, without anything to hold onto...it really scared me, Dad."

His dad said nothing at first, merely nodded and wrapped an arm around Harry's shoulders.

"I believe I understand," Severus replied, with an encouraging smile.

"You do?" Harry asked, tremulously.

"Yes." Severus wrapped an arm around Harry. "It feels unstable. Unsteady."

"I think so..." Harry frowned, just a bit. Was that it? With nothing to hold onto, and feeling like he'd fall and sink?

"Let's see," Severus mused. "There ought to be a way for you to put the two movements together..."

"Could I just try?" Harry asked, hopefully. "And-and you'll catch me, if I start to sink?"

His dad looked surprised, maybe even disbelieving that this could work, but he nodded. "Very well. Mind you, I will catch you immediately if you start to sink."

Harry returned the nod, then took a deep breath. He moved a few paces away from his dad, then lowered his frame until his face was touching the water. Slowly, he let one foot off the ground, then the second. Immediately, he began to kick, then made the arm movements he'd learned.

He was swimming! Really swimming! He continued to make the movements, propelling himself towards his dad until he reached him. It would only have been a few feet, but he had done it, hadn't he?

Severus was grinning as he pulled Harry into a hug. "Well done, owlet! That was an excellent first attempt!"

Harry grinned, nestling against his dad for several minutes. "I swam, didn't I? A bit?"

"You swam at least five feet, and I daresay more, if I hadn't caught you," he praised, releasing Harry to look into his face, and then hugging him again. "Would you like to try again? I can stand a bit further away?"

Harry let go of his guardian, nodding excitedly. "I'd like that, Dad!"

It was hard work, he realized, harder than just kicking or moving his arms. After all, he had to do both at once, and it took a lot of energy. Also, even though his robes kept him relatively warm, he could still feel the cold water. That probably made him more tired. Still, Harry persisted for awhile. Each time Harry reached his dad, he was rewarded with a big hug. It was only after he'd begun to yawn that his dad determined that the lesson was over.

"I dare say you're nearly dead on your feet, child. I'll give you a good bath, too, as I don't want to risk your falling asleep in the tub," Severus said, rather firmly for him, as they made their way to the shore. "But I am very, very proud of you."

"Thanks." Harry managed a grin. "How far do you think I swam, the last time?"

"Easily ten feet, perhaps fifteen. By the end of the holidays, you'll be quite good." Severus lifted Harry into his arms, then wrapped them both in a warm towel. "I believe you'll need a very long rest after your bath," he mused.

"I'm not-very tired," Harry protested, weakly. "I can walk, if you like."

"No." The words were firm, but his dad chuckled. "I'm carrying you straight into the castle, and into the bathroom. Once the tub is ready, you can relax while I give your hair a good cleaning." Harry felt his dad's hand on his head. "I dare say the child's ordinary shampoo doesn't work well enough with the salty lake water. I'll place an order for the one meant for swimming, but in the meantime, you'll use mine."

"I don't want it to get into my eyes," Harry murmured.

"It won't. You'll hold a wash cloth, and I'll be very careful," Severus promised.

The hot bathtub water felt especially wonderful compared to the cold lake water. Harry let out a sigh as his dad lowered him into the water, then placed his head on the pillow. He closed his eyes, glad to be truly warm, almost effortlessly floating in a way completely unlike how he'd been a good quarter hour earlier. Swimming was fun, but it was tiring. He opened his eyes again when Severus placed a hand on his shoulders.

"Here's the towel for your face," he said, softly. "I'll work on your hair, now."

"Oh. Okay." Harry pushed himself up, and held it against his face.

When they'd first started to live together, even before his dad had become his guardian, he'd washed his hair every day for the first week or so. Harry had been terrified, at first, because his aunt had been uncaring at best, and downright mean at her worst. Harry had never known she'd hated him so much as when she gave him baths, and his eyes paid the price on various occasions. Even though the water rinsed away the suds that got in, the pain remained long afterwards-and the memory to this day. But his dad wasn't like that. Harry thought his dad would do almost anything not to hurt Harry in that way-or in other many other ways that had just been a part of Harry's life with the Dursleys. His guardian loved him, and wanted him to be happy. So, even though Severus had to use adult shampoo, shampoo that didn't have a charm that prevented it from getting in his eyes, Harry wasn't afraid. Especially since he had a wash cloth to protect his eyes.

In fact, it felt really nice. His dad massaged his head the way the woman did when he had to get his hair cut, only it was actually even better. His strong hands worked the shampoo through his hair, then deep into his scalp. Harry let out a low murmur of contentment. It went on for some time, and then, his dad carefully rinsed away the suds. When he felt the warm water stop pouring down his head, only his dad's fingers, Harry was about to remove the wash cloth from his face.

"Hmm." His dad sounded...not angry, but not happy. "Harry, leave it up. We'll need to do it again, I'm afraid."

"I don't mind, really," Harry answered, truthfully.

Severus chuckled. "No, I'm sure you don't, owlet. Still, I would have hoped that once would be sufficient to remove the salt water." He sighed. "Very well, then."

It was even more wonderful the second time, and Harry could hardly keep his eyes open. His dad nearly had to carry him out of the bathtub, he was more than half asleep. Harry was aware of being dried off with a big, warm towel, and then a night shirt put on him. A hand held him upright, while another combed out his hair. The comb didn't snag, either. Then, Severus carried Harry onto the couch, and, before any chill could set in, wrapped them both in blankets. Harry curled into his dad's side, savoring the warmth, and then his arms around him.

"Love you, Daddy," he whispered.

"Love you, too, Harry," Severus murmured.

They both slept until dinner, and likely would have even longer if Severus hadn't roused Harry. He grumbled, just a little, unwilling to part with the warm blankets and his dad by his side.

Fortunately, his dad just laughed. "You'll be asleep again soon enough, I promise. For now, you need to keep up your strength and eat. And, owlet, I asked the house elves to prepare treacle tart for dessert."

Harry felt his eyes open widely. "Really?"

"Truly." Severus gave Harry's shoulders a squeeze. "Thought that might be enough to rouse you."

In truth, it was a toss up between staying on the couch wrapped in warm blankets, and the prospect of his favorite treat. But as his dad had already removed them from Harry's frame, the dessert was winning.

Besides, it wasn't cold in their quarters, not with the fire in the fireplace. Harry followed his dad into the kitchen, feeling a bit more awake with each step, and sat down at the table.

Supper was soup and grilled cheese sandwiches. Harry's stomach growled immediately, and he was eager to begin eating. Hot food after being in a cold lake-even though he'd gotten a nice bath afterwards-seemed perfect. Plus, there'd be treacle tart for dessert! It took a lot of control not to devour the food, something his dad had explained early on he mustn't do. It wasn't polite.

"I understand, Harry, that you were never allowed to eat enough," he'd explained, taking Harry into his lap.

"It was more than that," Harry had countered.

"Oh?"

"Dudley would get angry, sometimes, and throw over the table. Aunt Petunia wouldn't let me eat from the floor, so whatever I had eaten..." He'd looked down at the floor. "I got used to eating fast, just in case."

His dad had held him even more tightly in his arms. "I see." After a moment, he'd spoken again. "Dudley is not here, and neither you nor I will throw fits and topple over the table." Harry had managed a giggle. "So, from now on, you'll try to eat more slowly. Like a child, and not like a hippogriff?"

"I promise."

It had become easier, over time, for Harry to take his time and enjoy his food. Sometimes, like today, the old fear that something this good would be taken away from him, that he'd go to bed almost as hungry as before the meal begun-it entered into his head. Harry had to take several breaths and remind himself that he was safe, that the Dursleys would never be back, and his dad wanted him to eat his fill, and would only serve him good foods that he liked.

The soup was delicious, the vegetables flavorful and with just the right amount of crunch. The sandwiches burst with Harry's favorite kind of cheese, and the flavor exploded pleasantly in his mouth. After he'd finished the first, his dad asked if he'd like a second, and when he nodded, it appeared right away.

Harry still saved room for the treacle tart. As always, there was more than they could possibly eat, and he hoped that the remainder would not disappear into the kitchens. As though reading his mind, his dad spoke up.

"We'll hold onto the leftovers to enjoy for the next few days," he promised, looking at Harry with a smile.

Harry needed no bath after dinner, having already had a lovely one. There were still a couple of hours before his bedtime, and he wasn't as tired as he had been before. So, he and his dad remained in the sitting room, working on one of his puzzles, until Harry began to yawn.

"Time for bed?" Severus asked, eyebrows raised. "I know it's an hour before your bedtime, but if you're tired, there's no harm in retiring early."

"Okay," Harry answered, with a sheepish grin, and another yawn. "Can you stay with me? Like you did before? Please?"

His dad didn't sleep next to Harry most of the time, even though they cuddled together during the mornings, and for extra time on the weekends. But if Harry asked his guardian to stay with him the while night, he usually said yes.

"Very well." Severus smiled as he rose, then wrapped an arm around Harry's shoulders, holding him close. "After we brush our teeth, we'll meet in your room."

Harry gave a toothy grin, causing his dad to chuckle. "Yes, all of your teeth, owlet!"

Once they were in Harry's bed, and the lights were off, he found he couldn't sleep.

"Dad?" he whispered.

"Yes, child?"

"C-can I ask you something?"

"Yes, of course." The light went on again, and Severus pressed himself into a sitting position. "What's on your mind?"

Harry chewed on his lips. "Were you upset that-that I couldn't let you hold me in the water?"

Severus shook his head, the movement firm. "Not at all."

"Really? Even though I couldn't do what you wanted?" Harry could feel his throat beginning to hurt.

"Owlet." His dad placed his hands on Harry's shoulders. "If anything, I am proud of you. Yes, I expect you to obey me, but I don't expect you to do so without thinking. If I am trying to teach you something, and you are truly scared or merely uncomfortable, then I want you to tell me."

A few tears fell down Harry's face, and his dad immediately brushed them away. He murmured soothing sounds as he held Harry against him.

"Besides," he added, thoughtfully, "if you had allowed the intermediary stage, you might not have been able to swim so soon."

Harry took a deep breath, as much to fill his lungs as to inhale the familiar scent of his adopted dad.

"If you disobey me, I shall let you know," Severus continued, gently, "but you have been a very good child, owlet."

"Except when I used a school broom without your permission," Harry countered, softly.

"Ah, but you were pressured by an adult to do so, and received an appropriate punishment," he reminded Harry. "Moreover, I won't stop loving you simply for disobedience. Not that I am giving you leave, mind," he added, gently tapping Harry on the nose.

"I understand," Harry murmured, yawning.

Severus wrapped his arms around Harry. "I love you, owlet."

"Love you too, Dad," Harry whispered.

Note:

I reread parts of "Harry Potter and the Goblet of Fire" to make this chapter consistent with canon. I was rather surprised to find that JKR did not describe much of the lake insofar as how it appeared to an observer. For example, did the lake have any waves? Such occur in natural lakes, and this one is magical. How far does a person have to travel before being entirely submerged? (To be fair, Harry did have to walk at least long enough to finish chewing the Gillyweed before needing to submerge himself in order to breathe...) She spent most of her focus on the interior of the lake, which makes sense according to the storyline, but rather makes it more difficult for me, as Harry and Severus will generally stay at the surface.

I taught myself how to swim when I was nine. Using goggles gave me the confidence to make the leap of putting the steps I could perform individually together that swim lessons simply didn't. But I remember that being held up, without anything to hold onto, was that worst. I suppose that there's a practical reason for doing it, in order to put the steps together without actually having to swim, but it definitely didn't work for me. So, I had Harry have the same reaction.

Online research says that schools in England teach swimming. This might not have been the case in the 1980's. Not that it would have helped Harry with being able to breathe underwater for an hour! At least, in canon, he could manage to stay afloat.