Shimmer
Disclaimer: I am not Nickelodeon or the awesome people responsible for Avatar. I am significantly less awesome, and only own the first season on DVD.
There are things that they'll have to do soon, but moments of peace are too rare not to be grasped with both hands. For now she can let the river carry her along, with the sun on her face and her element at her back. Water isn't steady like earth; it changes of its own accord, with no aid from a bender.
Water is almost alive, more than the other elements; that's why she can heal. Water is a part of everything that lives and just as Toph can see through her element, Katara can sense the currents in a body by the liquid inside it. Slipping beneath the surface of the river is easy and natural as breathing, and thus submerged that sense is magnified; she can feel Aang, faintly, waterbending in the shallows, feel the water rising to his call. Appa is downstream, and her lips quirk involuntarily when she realizes she can feel the low throb of his pulse through the currents. She's running out of usable air, and draws a little more oxygen from the water around her. There are enough plants in the deeper water that it's easy. She spares a moment to enjoy the bright, quick fish and the tangled net of light cast over the sandy riverbed. No need to bother looking for Toph or her brother; Toph wouldn't come near the water. The run-in with the serpent at the Pass was quite enough for her, and she doesn't like being truly blind.
Sokka isn't in the water, either – then suddenly he is, and the air she'd been holding in her lungs is startled out by a pair of strong arms around her waist. Waterbender or no, real water isn't safe for her to breathe, and she fights the need to inhale. She struggles briefly (an automatic reflex after so much fighting) but stops to gasp for breath when they break the surface.
"What were you doing? I thought you were drowning or something!"
After Sokka releases her, Katara turns to glare at her brother.
Aang has stopped waterbending, the thin ribbon of water falling to rejoin the river. Toph looks confused – she can't 'see' them in the water, just felt, through the earth, Sokka's sudden panic before he leaped into the river.
"Can a waterbender drown?" Aang sounds genuinely curious.
"Uh..." Clearly that had not occurred to her brother.
Toph isn't curious, just nettling. "Can you set a firebender on fire?"
Katara just looks at him, and he sinks into the water until only his eyes and his ponytail are above the surface.
Appa is swimming back to them, clearly aware that the talking means it's time to go. Momo is perched on his head, looking for all the world like he thinks he's captaining a ship. The flying bison and his passenger are almost back to them when Katara bends a sphere of water over her brother's head and lets it drop, cutting toward the shore while he sputters.
"Can't a guy get any appreciation around here?!"
Sokka's irritated query is immediately followed by the loud slurp of Appa's tongue.
"... That is not what I meant."
