Northern Glaciated Plains Ecoregion Key
| Stream 1st-2nd order or <30 miles long | Northern Glaciated Intermittent Stream | ||
| Stream 3rd-5th order or 30 - 100 miles long | Northern Glaciated Prairie Stream | ||
| River >5th order or >100 miles long | Medium Prairie River | ||
| River >5th order and >200 miles long and a direct tributary to the Missouri River (Milk or Marias Rivers) | Large Prairie River | ||
| The Missouri River downstream from Great Falls | Large Valley River |
