The female's body measures 15 - 22 mm, the male's from 10 to 13 mm. The species of both sexes are dark chocolate-brown to greenish in colour, with a conspicuous white or cream stripe along each side. In some species, particularly the young, the stripes are fully absent, and such species are coloured yellowish-brown.
The raft spider is dependent on slow moving or standing water. It inhabits lowland fen, grazing march areas, and wetland forests and orchards. Populations are found throughout Europe and Asia.
The raft spider builds no shelter and perches for hunting and basking in the emergent vegetation. With a dense system of sensory hairs, the raft spider can move rapidly rapidly through the water and hide under water from predators. Adult spiders are active from June to August, feeding on aquatic insects, tadpoles, and sticklebacks.