Dead-end

I stopped through the park on my way home and noticed something odd. There were about 30 fish "swimming" in this small channel. They weren't really going anywhere, just huddled together. They didn't even move when I approached them. The channel looked like it dead-ended but I think it was more of a tunnel into another pond. I have no idea what they were doing or why they were doing it. I'd never even seen them in this part of the pond before. It was weird.