Sorry, no photo. I have several half wine barrels in which I grow water plants (iris, water lilies, water hyacinths) I recently had to move the barrels to another location, so emptied them out, saving all my mosquito fish and water. I noticed some 3/4 inch bugs in a couple of barrels; I have never seen them before, and those barrels did not seem to have any fish OR mosquito larvae. At first, I put the bugs back in the barrels but when I realized I wasn't seeing any fish with them, I became concerned that they might be eating the fish. The bugs were in the muck at the bottom, although they might just have been hiding there. All that I saw were about 3/4 inch long, maybe 1/4 inch wide, and I think they were brown, although by the time I found them at the bottom, most had some algae wrapped around them. Any ideas what they might be? Thanks!
CLOSED: Water bugs!
Okay, some research has answered my question: they are dragonfly larvae! And the do eat mosquito larvae AND small fish. Images: