Severus rolled his trousers midway to his knees and sat himself down on the edge of the dock. The lake was a pool of ink, black as his robes. Ripples edged to the reed-choked shore, radiating from the slide of his feet beneath the water's calm.
A fat bubble broke the surface, followed by a flurry of dozens more, tiny as champagne bubbles. They floated like stars until disturbed by the emergence of a dark crown of hair, slick and gleaming in the wan moonlight.
"Join me," Harry said, hanging in the water for a long moment before he surged up to prop his arms on the planks beside Severus. Droplets slid from his naked skin, pooled dark on the smooth wood. He looked for all the world like a muggle merfolk idealised--his chest smooth and strong and perfect narrowed down to ghostly mystery beneath the water. But if Severus looked carefully, he could see Harry's legs gently scissoring.
"I'd rather watch you swim," Severus said.
"Is that really what you'd rather do?" Harry lifted himself out of the water, lean muscles of his arms going taut as he held himself high enough that his mouth flirted near Severus's shoulder.
"For the moment." This was their life now, simple, quiet, free to swim naked in the middle of the day should they wish it.
"Liar," Harry said. He sank back into the water, vanishing for the blink of an eye before bobbing to the surface again. His hand, chill from the swim, curled around Severus's ankle and tugged. "Come in or I pull you in. Your choice."
Severus yanked his leg free. "Offering choices that aren't. Like father like son." He winced as soon as the words spilled free into the quiet of the night, waited for the flash of anger or pain in Harry's eyes he'd seen so many times before.
But Harry's mouth just pulled into a smile and he caught Severus's leg again, grip firm and unyielding. He had changed so much in the past few years while Severus struggled to keep pace. Some days he worried that Harry would tire of this game, tire of him and his inability to hold his tongue. "You'll complain, but secretly you want me to." Harry braced himself against one of the moss-slick pylons, the threat of hauling Severus into the lake looming as black as the water. "Last chance...."
"Very well." Severus shifted, lifted his hands to undo the row of buttons at his throat, and before his fingers had finished with the second, the world dropped out from under him.
Watery dimness closed in, his robes ballooning around him one moment and a smothering weight the next. He choked on a mouthful of water before instinct snapped his mouth shut, and he jerked away from the press of fingers at his mouth. Harry's fingers swept over his lips again, air gathering in the wake of his touch. Severus's feet found the slick bottom of the lake and he swayed from the push of water and the stronger push of Harry's foolish impulses. He let Harry strip him down, free his robes to the whim of the water.
"Not so bad, is it?" Harry asked, pulling him away from the shore to deeper water where they floated together, connected sometimes by only the briefest touch of their fingers.
In the cool, clinging darkness, Severus permitted himself to agree.