Hydrological code United States United States

| Name_ | Level_ | Digits | Average_size_square_miles | Number_of_HUs_approximate | Example_name | Example_code_HUC |
|---|---|---|---|---|---|---|
| Region | 1 | 2 | 177560 | 21 | Pacific Northwest | 17 |
| Subregion | 2 | 4 | 16800 | 222 | Lower Snake | 1706 |
| Basin | 3 | 6 | 10596 | 370 | Lower Snake | 170601 |
| Subbasin | 4 | 8 | 700 | 2200 | Imnaha River | 17060102 |
| Watershed | 5 | 10 | 227 (40,000–250,000 acres) | 22000 | Upper Imnaha River | 1706010201 |
| Subwatershed | 6 | 12 | 40 (10,000–40,000 acres) | 160000 | South Fork Imnaha River | 170601020101 |