The waterways, with their distinct mountain stream character, play an important role right across the Harz. In comparison with the other natural regions of Lower Saxony, they are still very natural and varied, and the water is very clean. As a result of the high water velocity of the Harz streams, flowers rarely gain a foothold in the water. Even the animals in these streams need to be well suited to high velocities. Only a few species, such as fish, swim actively against the stream. The most common species are brown trout (Salmon trutta forma fario) and bullhead (Cottus gobio). Much richer in variety, by contrast, is the range of species in the system of crevices under the streambed. In addition to the insects and fish hatchlings that thrive here, may be found protozoons, flatworms (Turbellaria) and water mites (Hygrobatoidea). Other species of animals cling fast to the stones, e. g. caddis fly larvae (Trichoptera) and snails, or can only live in the reduced water velocities on the bed of the stream or on stones by having flat body shapes, e. g. stonefly larvae. In the calmer parts of the stream, behind stones or in blankets of moss, there are also water beetles (Hydrophilidae) and small shrimp-like amphipods.