The crew had shore leave and went sailing on a lake. Noticing that some of his friends had jumped out to swim, Data decided to join them. "Come on in, the water's fine!" Geordi called out.
Data nodded, and without even removing his shoes jumped into the water. But he didn't come back up. There weren't even bubbles. "Data? DATA?!" Geordi shouted, but there was no response. He stuck his head under to locate his friend, and saw him walking along the bottom. Data looked up at Geordi from below, and continued walking. Geordi resurfaced, laughing at Data's unfortunate miscalculation.