Riverweed grows submerged (up to 75+ cm deep) to seasonally exposed on cobbles and bedrock substrate in fast flowing, relatively large streams or rivers. It often occurs in rapids (New York Natural Heritage Program 2008). Fast-moving streams, especially rapids (Crow and Hellquist 2000). In rapidly flowing water (Gleason and Cronquist 1991). On rocks in streams (Fernald 1970).

Confined river The aquatic community of relatively large, fast flowing sections of streams with a moderate to gentle gradient.

Rocky headwater stream The aquatic community of a small- to moderate-sized perennial rocky stream typically with a moderate to steep gradient, and cold water that flows over eroded bedrock, boulders, or cobbles in the area where a stream system originates.

(Cladophora sp.)