Hydrology Report
A hydrologic unit code is a sequence of numbers or letters that identify a hydrological feature like a river, stream, snow covered area, or a watershed (also called a drainage basin). The USGS maintains a hierarchical system of hydrologic units broken up into regions, sub-regions, accounting units, and cataloging units. Each hydrological area has its own Hydrologic Unit Code (HUC). View hydrology reports by HUC code to get a closer look at river and snow conditions across the US.
| Name | Level | Digits | Average Size (Square Miles) | Number of Areas | Example Name | Example HUC Code |
| Region | 1 | 2 | 177,560 | 21 | Pacific Northwest | 17 |
| Subregion | 2 | 4 | 16,800 | 222 | Lower Snake | 1706 |
| Basin | 3 | 6 | 10,596 | 370 | Lower Snake | 170601 |
| Watershed | 4 | 8 | 700 | 2,200 | Imnaha River | 17060102 |
Regional Streamflow and Snowpack Comparison
