Haliplidae

The Haliplidae are a family of water beetles who swim using an alternating motion of the legs. They are therefore clumsy in water, and prefer to get around by crawling. The family consists of about 200 species in 5 genera, distributed wherever there is freshwater habitat; it is the only extant member of superfamily Haliploidea. They are also known as crawling water beetles or haliplids. Read more at Wikipedia