Watersheds 101

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 basin

How are watersheds organized?

Watersheds are organized by Hydrologic Unit Codes or HUCs (pronounced "hucks") delineated by the United States Geological Survey 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 United States is broken up into 19 water resource regions (HUC 2's) and each catchment area scales down into smaller and smaller watersheds, with a HUC 12 being the smallest unit.

The amount of digits in a HUC number also indicates the scale of a watershed. Larger numbers equal smaller HUCs, a HUC 12 (041000070603) is much smaller than a HUC 2 (04).


The HUC 12 boundary is commonly used at the local level for watershed management due to its smaller scale. For example, the HUC 12 Kyle Prairie Creek spans a little over 10 miles across from east to west on the Mercer County and Van Wert County border. 

Use the tool below to find your local watershed and see the water quality issues pertinent to your area. 


Find your watershed