To provide good habitat, rivers and streams need a mix of deep and shallow areas, known as pools and riffles. These provide different habitats for insects and fish. Many insects live their entire lives in a specific site, such as a riffle. Fish may use different habitats during different life stages, and depend on different types of insects during various life stages.
All streams need some solid material such as cobble, submerged logs or snags to provide habitat for certain insects, as well as a spawning area for some fish species. Generally, small streams need more substrate as a percentage of stream bottom than larger waterways.
Stable Stream Banks
Usually anchored by tree roots, stable banks are important because they keep dirt from eroding into the stream where it can smother bottom-dwelling insects or silt over cobble bottoms. Also, grains of sediment increase the natural erosion power of moving water. A ton of sediment added to water can cause several tons of erosion in the stream channel.
Forests were the natural environment for most Mid-Atlantic streams, and they provide a host of stream benefits. Their leaves form the base of the food chain in small streams, their roots stabilize streambanks, their shade moderates stream temperature, and they contribute large woody debris. In addition, they filter pollutants from both runoff and shallow groundwater before it can reach the stream.
Lots of Large, Woody Debris
Fallen logs and limbs create channel diversity, forming pools and riffles. As they rot, they add nutrients to the water which, like leaves, fuel stream productivity