You know, now I'm not so sure... but it seems the closest thing from what I found on the net.
It swam forwards, not in a smooth fashion - I could see by the slightly jerky movement that it was propelling itself forwards with its legs. And it would land on the side of the bucket and peck at the walls. I haven't seen it since. No forked tail. It mostly hung out in middle and top parts of the water when I saw it, and not on the bottom, but then it did go to the bottom I wouldn't know - it would blend in. It also seemed to dislike light, or at least a lot of it. It looked a lot like the drawing on the top left of this page http://www.bugsurvey
I don't mind the larvae, I just mind the flying adults. The thought of something someday crawling out of the bucket to fly around the house freaks me out.
I already have my pond snail platoon, so the algae is taken care of :P