The predaceous diving beetles in the genus Thermonectus are some of the most elegant swimmers I’ve ever seen. They paddle around serenely in open pooled areas of desert streams and you can look down into the water and see dozens of them calmly swimming about at all depths. They accomplish their smooth, beautiful swimming because they are completely smooth and slippery and water just slides right over them. But they also have enormous, oar-like hind legs, easily visible in this photo:
Wish I could swim as gracefully as these beetles do. Apparently I need to grow some different legs!