Watersheds & Lake Erie

What is a Watershed?

A watershed is an area of land that drains water from tributaries and rainfall to a common body of water. The term watershed can be used interchangeably with basin or catchment, and there can be several watersheds nested within larger catchment areas.

catchment example

How are watersheds organized?

Watersheds are organized by Hydrologic Unit Codes or HUCs (pronounced "hucks") delineated by the United States Geological Survey (USGS) using a nationwide system based on surface hydrologic features. These hierarchal levels of watershed classification contain a series of numbers from 2 to 12 digits used to identify any hydrologic area. The amount of digits in a HUC number also indicates the scale of a watershed. Larger numbers = smaller HUCs. 

Hydrologic Unit Codes or HUC

6-level hierarchal levels of watershed classification

For Example: HUC 12 (041000070603) is much smaller than a HUC 2 (04).

The United States is broken up into 19 water resource regions (HUC 2) and each catchment area scales down into smaller and smaller watersheds, with a HUC 12 being the smallest unit. The HUC 12 boundary is commonly used at the local level for watershed management due to its smaller scale. 

 US water regions and watersheds

Narrowing Down the Watershed

The Great Lakes Watershed

great lakes watershed

The Great Lakes Watershed is the largest system of freshwater in the world.

Drainage basin ~295,710 mi2

Home to 37 million people

The world's 3rd largest economy

One of the richest and most ecologically diverse ecosystemon the planet 

Lake Erie Watershed 
Lake Erie Watershed

Home to 12 million people (1/3 of the total population in the great lakes watershed)

2nd smallest great lake

Smallest by volume




Shortest water retention ~2.6 years

Fertile soils and intensely farmed, exposed to the greatest effects of urbanization and agriculture

The Lake Erie Basin 

Lake Erie Basin


Lake Erie has three primary basins: Western, Central and Eastern. The Western Basin, which extends from Toledo to Sandusky, is the shallowest of the basins with an average depth of only 24 feet. The Central Basin, extending from Sandusky to Erie, Pennsylvania has an average depth of 60 feet. The Eastern Basin’s average depth is 80 feet. Lake Erie’s maximum depth is 210 feet in the Eastern Basin

The Western Lake Erie Basin
Western Lake Erie Basin


Home to 2 million people over 29 counties.

City of Toledo drinking water.

Drains 7,000,000 acres across the tri-state area.

Drains into the shallowest portion of Lake Erie,

Comprised of ~80% agriculture


western lake erie basin

The Western Lake Erie Basin (HUC 6) can be further narrowed down to additional subbasins, including the smallest unit (HUC 12) which is used at the local level for watershed management due to its smaller scale. Our OSU Water Quality Extension Associates commonly use these units to implement and monitor common water quality conservation practices on the field scale.