a Turtle, I hadn't thought of a turtle. There's no shade at all though, and I think one would need a way to get out of the sun.
I cleaned out the filter on that pond this morning and it too was full of the things. They don't swim around if they can help it but they can really move through the water to get back to the muck or hidden somewhere. This pond turned green about 8 months ago after being clear for a few years. I can't get it to clear again and I'm wondering if these things are mucking around and stirring things up? Also, every day there are chewed leaves from the aquarium grass floating. I thought that might be the fish going in there after the bugs, or it is the bugs themselves. Something is chewing the grass blades off so that every day I clean out lots of floating grass.
I might try and catch a couple of the cichlids downstairs and see what they do up there. They are really fast so they could catch the bugs (or the guppies) if they are interested.