When water is not flowing, it may remain in isolated pools or surface water may be present. Gradient is low. The substrate consists of sand and mud. Oxygen deficits may occur. Gradient high, water velocity fast.
Water flows throughout the year.
Substrate consists of rock, cobble, gravel, and sand. Dissolved oxygen content high. Vegetation remains upright and visible throughout the year. This includes ponds, borrow pits, small reservoirs, and open water areas within a marsh or swamp. Flooding controlled by pumps or siphons in combination with dikes or dams.