Hmm, well I use to keep a few bottom feeders, mind I bought them at the pet store and didn't fish them out of a park! There are types of food on the market that are made to sink instead of floating on the surface. These are made for bottom feeders and contain the sort of things they need to survive. Still, if it's form the wild that would be the best place for it so unless you don't think it will make it iout there, best to return it.