Scientific Importance of Small Streams and Wetlands

Our nation’s rivers, from the Shenandoah to the Sacramento, owe their very existence to the seemingly insignificant rivulets and seeps that scientists call headwater streams. The origins of rivers are often anonymous, unnamed networks of seeps, springs, and wetlands whose waters join together above and below ground as they flow downstream.

As other tributaries join them, small streams grow larger, eventually earning the title “river.” The character of any river is shaped by the quality and type of numerous tributaries that flow into it. Each of the tributaries is, in turn, the creation of the upstream waters that joined to form it.  Each small stream and river varies in shape and character, depending on the climatic region.

Yet, like the capillaries that connect to our bloodstream, the health of these small streams and wetlands is critical to the health of the entire river network. In our report, Where Rivers Are Born, American Rivers has worked with the academic community to document and explain the robust science that demonstrates the critical nature of small streams and their network. Based on the most recent research, this paper summarizes the scientific basis of understanding how small streams and wetlands mitigate flooding, maintain water quality and quantity, recycle nutrients, create habitat for plants and animals, and provide other benefits. These benefits are numerous, including:


Small streams and wetlands offer an enormous array of habitat for plant, animal, and microbial (bacteria and fungi) life. These small freshwater systems provide shelter, food, protection from predators as well as spawning sites and nursery areas. In fact, many species depend on small streams and wetlands at some point in their life history. Amphibians such as frogs and salamanders rely heavily on these aquatic systems for some part of their life cycle. While fish such as trout require these cool, small streams for both habitat and spawning sites.


Headwater streams house a large number of unique taxa. A recent study suggests headwater streams support over 290 taxa, some of which are unique to only headwater stream habitats and are not found in larger rivers.

Food web

Headwater streams provide a rich resource base for productivity of stream food webs, providing food for animals living within the stream as well as food for animals living downstream.  Animals living within the stream often also become a food resource for those animals living in the landscape. Specifically, birds, snakes, and bats often consume stream animals including insects, salamanders, and fish for prey. Headwater streams are not only important for stream food webs but for terrestrial food webs as well.

Clean Water

Scientific research has demonstrated healthy headwater streams are critical to healthy downstream streams, rivers, lakes, and estuaries.  Headwaters have proven especially important with regards to their significant capacity to store and transform nutrients (nitrogen and phosphorus). Without this function, downstream waters would receive elevated amounts of nitrogen and phosphorus that cause algal blooms and low oxygen (eutrophication) in reservoirs and coastal areas.  Areas with low oxygen, referred to as “dead zones” have detrimental effects on fisheries in well-known areas such as the Gulf of Mexico and the Chesapeake Bay.

Flood control

Headwater streams absorb significant amounts of rainwater, runoff and snowmelt before flooding.  A key feature of the streams absorption capacity is the natural, rough streambed.  Friction with a stream’s gravel bed, rocks, and dams of leaf litter and wood slow downstream flow allowing water to seep into soil banks, thereby recharging groundwater and reducing flooding.  These benefits provided by headwater streams are vital to all communities.


Report: Where Rivers Are Born: The Scientific Imperative for Defending Small Streams and Wetlands