What is a watershed?
A watershed, also called a drainage basin, is all of the land and water
areas that drain toward a particular river or lake. Thus, a watershed
is defined in terms of each selected lake (or river). Large watersheds
are composed of smaller areas called subwatersheds. For example, the
Mississippi River has an extremely large watershed, encompassing most
of the central United States. Lake Itasca, Minnesota, on the other hand,
has a small watershed. As the source of the Mississippi River, Lake
Itasca's drainage basin is considered a sub-watershed of the entire
Mississippi River basin.
Why should I care
The water quality of your lake is affected by activities upstream or
upland of the lake within the watershed, so it is important to know
the geographic area encompassed by the watershed surrounding your lake.
Especially important are the watershed processes that affect how water,
sediment and other materials get transported to the lake. Looking at
both natural processes and human influences from a watershed perspective
is vital for dealing with concerns such as lakes that are unsafe for
swimming or declining fish stocks. Check out the Environmental Protection
Agency watershed web site (http://www.epa.gov/OWOW/watershed/)
to learn more about watersheds and why it is important to know about
What are the sources
of water to lakes and streams?
Water runs over land surfaces (overland flow) and into stream channels
when it rains, when snow melts, or during irrigation. Water also seeps
into and through the soil and underground (groundwater flow). Groundwater
does not necessarily always follow the same watershed boundaries as
surface water. In fact, groundwater flowing into lakes can sometimes
originate from outside the watershed. Plants intercept water on their
leaves and take up water from the soil. Land uses can alter the natural
flows of water. Impervious surfaces such as parking lots, roads, and
rooftops increase the velocity and amount of stormwater flow into lakes
How do watershed
managers determine watershed boundaries?
Watershed managers use topographic maps to identify ridges and other
high points that separate one watershed from another. Topographic maps
show the contours of the land's surface. By connecting the high points
on the map, managers include all the drainage that flows into a lake
and exclude any drainage flowing away from the lake. U.S. Geological
Survey (USGS) topographic maps are available from bookstores, libraries,
and can be ordered from USGS Information Services (1-800-USA-MAPS or
The Land Information Management Center has maps online that allow you
to view major watersheds and subwatersheds at the "Index of Minnesota
The Minnesota Department of Natural Resources also has watershed maps
online at http://www.dnr.state.mn.us/waters/rivers_and_streams/wsheds.html.
Who can I contact
if I have questions or a problem related to watersheds?
Check your local listing, the Minnesota Shoreland Management Resource
Guide Web site, www.shorelandmanagement.org,
or the Web site for:
- Your county Soil
and Water Conservation District (SWCD)
- Your county Water
- Minnesota Department
of Natural Resources (MDNR) www.dnr.state.mn.us
- Your county Planning
- United States Geological
Survey (USGS) www.usgs.gov
What are some additional
resources about watersheds?
- Shoreland Landscaping
Series: A guide to natural landscaping and revegetation for enhancing
lake quality. 1999. University of Minnesota Extension Service,
- A Citizen's Guide
to Lake Protection.
1985. Minnesota Pollution Control Agency and Freshwater Foundation
- A User's Guide
to Shoreland Property. 1999. Aitkin County and the Mississippi
- Minnesota Lake
And Watershed Data Collection Manual. 1994. Minnesota Pollution