I recently found some little buggies in a vegetation-heavy lake. I couldn't get a picture that looked like anything more than a little red dot. They were probably a millimeter across, fire-engine red, and swam fairly quickly (though not very straight). Upon closer inspection, they had about 6 little legs, all near one end. They looked almost like really agile ticks without the icky head/mouth part, but they were definitely aquatic, and I found them in multiple spots.
I know this isn't a bug forum, but Google has been unhelpful, and I figure there has to be somebody on here who knows what these rather distinctive bugs are.