The naiad moved in shortly after Sid finished his house, that first summer, a week after he filled the pool. He noticed some splashing one morning while he was eating breakfast, and when he went outside to investigate, she popped her head up out of the water, clung to the side of the pool, and hissed at him. “Uh,” Sid said, still holding a slice of toast in one hand. Dew from the grass chilled his bare feet. “Are you—hi?”

It starts with Sasha's neighbour worrying about the stupid fish. When Sasha finds out what's behind that, it ends so, so much worse for him... Or: Putting "ovi" into "oviposition" ;) (~8k of Ovi getting tentacle dicked down + oviposition, the fic's basically in the tags, and what is advertised there is exactly the fic, you do the math)