Three ideas on the fish.
One - Someone put some there.
Two - Bird grabbed a pregnant one and then accidentally dropped it in there before eating it.
Three - When the waters from Noah's flood receded, a few were trapped there.
Personally, I leaning towards option 1. If I come visit, will you take me there?
The odd this is I have been there before and have never seen fish there and especially not bigger ones like that. I think it is more likely someone put them in there like you said.
Yeah I will take you there. There are a couple other super cool spots as well!