What is a Reference Watershed?
The NNRW defines reference watersheds as those minimally disturbed by human activity preferably in an area
protected from human-induced changes. References watersheds can be used to measure changes in soil chemistry,
vegetation, water quality, and biology through time as well as to compare to disturbed watersheds.
The network is currently composed mainly of U.S. Geological Survey and U.S. Environmental Protection Agency
watersheds however, as the network expands watersheds will be added from other Federal, State, tribal,
interstate, academic, local and private sector organizations that choose to participate.
The "Watershed Search" section of the website allows users to search the entire network database. The
database includes many types of reference watersheds; some are considered reference based on low hydrologic
disturbance, others based on land use disturbance, and others based on water quality, stream biology, or
some combination of criteria. Results of users searches can placed into context with all watersheds in
the database on cumulative frequency diagrams like the one to the right.
The "Core Watersheds" section of the website allows users to search a subset of the NNRW database that
contains only the most pristine watersheds based on
specific land use criteriaLow hydrologic disturbance (dams, water withdrawal, pollutant
discharge, etc.); 0% Row Crops; < 5% Pasture; 0% High Impact Development; 0% Medium
Impact Development; < 10% Total Development (High + Medium + Low); Natural vegetation +
Barren Land > 75%
Core watersheds also have stream discharge data available.
Select the "Core Watersheds" tab to explore the most pristine watersheds in the network or select the
"Watershed Search" tab to search the entire NNRW database of reference watersheds and access data available
for those sites.