| 1 Northwestern Great Plains Ecoregion |
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Go To 2 Below |
| 1 Northern Glaciated Plains Ecoregion |
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Go To 4 Below |
| 1 Montana Foothills and Valleys Ecoregion |
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Go To 5 Below |
| 1 Middle Rockies and Isolated Mountain Ranges |
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Go To 7 Below |
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Northwestern Great Plains Ecoregion |
| 2 |
Stream 1st-2nd order or <30 miles long |
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Go To 3 Below |
| 2 |
Stream 3rd-5th order or 30 - 100 miles long |
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Great Plains Prairie Stream |
| 2 |
River >5th order or >100 miles long |
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Medium Prairie River |
| 2 |
River >5th order and >200 river miles long and a direct tributary to the Yellowstone or Missouri River (Little Missouri, Tongue, Bighorn and Powder Rivers) |
|
Large Prairie River |
| 2 |
Yellowstone River downstream from Billings or the Missouri River downstream from Great Falls |
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Large Valley River |
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| 3 |
Perennial 1st or 2nd order stream above 1000m elevation in the Wolf Mountains, Powder River Basin or Missouri Breaks |
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Great Plains Perennial Spring |
| 3 |
Small (< 100m2 in area), low gradient intermittent pools separated by long breaks of dry stream bed, typically lacks downstream connectivity to a large mainstem river |
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Great Plains Intermittent Stream |
| |
Northern Glaciated Plains Ecoregion |
| 4 |
Stream 1st-2nd order or <30 miles long |
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Northern Glaciated Intermittent Stream |
| 4 |
Stream 3rd-5th order or 30 - 100 miles long |
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Northern Glaciated Prairie Stream |
| 4 |
River >5th order or >100 miles long |
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Medium Prairie River |
| 4 |
River >5th order and >200 miles long and a direct tributary to the Missouri River (Milk or Marias Rivers) |
|
Large Prairie River |
| 4 |
The Missouri River downstream from Great Falls |
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Large Valley River |
| |
Foothills and Valleys Ecoregion |
| 5 |
1st order, origin from Valley Floor groundwater output |
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Spring Creek |
| 5 |
1st-2nd order or <30 miles long |
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Headwaters Foothills River |
| 5 |
3rd-4th order or >30 and <60 miles long |
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Go To 6 Below |
| 5 |
4th-5th order, >60 miles long and a direct tributary to the Yellowstone or Missouri River |
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Intermountain Transitional River |
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| 6 |
Cool-cold water tributaries that originate in the foothills and flow out to prairie rivers that are too warm to support coldwater fisheries |
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Small Transitional Foothills River |
| 6 |
Coldwater tributaries that flow to foothills and valley intermountain transitional rivers that maintain coldwater fisheries |
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Small Foothills River |
| |
Middle Rockies and Isolated Mountain Ranges Ecoregion |
| 7 |
1st - 2nd order or <15 miles long |
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Go To 8 Below |
| 7 |
3rd - 4th order or 15 - 60 miles long |
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Mountain Stream |
| 7 |
5th order or >60 river miles and a direct tributary of the Intermountain Transitional River |
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Small Transitional Foothills River |
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| 8 |
1st or 2nd order, elevation >2400m, hydrology driven by alpine snowmelt |
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Alpine Stream |
| 8 |
1st order, elevation from 1500 to 2400m, hydrology fed by ground water discharge |
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Mountain Spring |
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