Common Terminology


The upper reaches of a stream, near the stream’s origin.

Many streams and associated wetlands in headwaters are small and do not appear on maps, yet are vitally important to the health of the larger stream system. 


Areas of land covered with trees. Watersheds with more forested land tend to have better water quality.* Healthy forests act as a filter to keep pollution out of water. Strong roots hold soil in place as it rains. Healthy soils provide a place for rain and melting snow to soak into the ground, slowing the flow of runoff and absorbing pollution carried in the water. When forests are disturbed and degraded by clearing, excessive browsing by deer, or forest pests, it is easier for sediment, nutrients, and other pollutants to flow into streams and harm water quality.

Streamside areas

Streamside areas are an important part of stream systems and are sometimes called stream or riparian buffers. Streamside areas with a healthy mix of trees and shrubs support stream health and clean water by slowing runoff, filtering pollution, preventing soil erosion, and shading the stream to keep waters cool for fish. These areas can also absorb and slow flood waters, which protects property and human safety. Forested streamsides play an important role in maintaining clean water, even in watersheds that are mostly forested.

Streams and rivers

Streams and rivers are natural waterways with a detectable current and a defined channel. Streams may flow year-round, seasonally, or only during times of heavy rain or snow melt. Water that ends in streams comes from runoff from the land as well as groundwater. Streams and rivers move water and sediment across a watershed. A stream is a dynamic system, shaped by water, the organisms that live in it, and the sediment it carries.


All of the lands and waters that flow into a common body of water. Because water always flows downhill, the edges of a watershed are typically defined by ridges and hills. No matter where you go, you are in a watershed, and your actions can have an impact on streams and wetlands miles away.


Wetlands (swamps, marshes, bogs, and similar areas) are transition areas where the water table sits at or near the ground surface and which have plants adapted to the soggy conditions. Wetlands slow the flow of water and temporarily store it before releasing it downstream. Wetlands can hold a lot of water, which is why they help reduce flood risk. Wetlands also play an important role in recharging groundwater and maintaining stream flows during droughts.