Rivers and streams (PDF) are generally characterized by surface water flow that has produced a defined channel or bed. Rivers and streams essentially function as a drainage system that transports water, sediment, and dissolved nutrients across the land’s surface toward the sea.

They also provide important habitat elements for fish and wildlife species. Many factors can affect the function and characteristics of a river or stream system, including: precipitation patterns, geology, topography, and human activities such as dams, dikes, gravel extraction, and removal of riparian vegetation.

Containing Water
A channel or bed does not need to contain water year-round to be considered a stream. Streams can also include drainage ditches or other artificial water courses where:

• Natural streams existed prior to human alteration
• The water way is used by salmon fish populations
• The water course flows directly into a shellfish habitat conservation area

Benefits
River and Stream corridors perform a variety of beneficial functions, including:

• Fish and wildlife habitat
• Flood and storm water storage
• Groundwater recharge
• Recreation, education, scientific study, and aesthetic values