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Low-Head Dam Danger Zones
Low-head dams are among the most deadly hydraulic features in moving water. The recirculating hydraulic traps victims regardless of swimming ability. MANDATORY PORTAGE.
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DANGER: Low-Head Dam — Rainbow Dam (Great Falls)
Missouri River · MT
Hydraulic Recirculation Zone — Extremely Dangerous
Low-head dams create a submerged recirculating hydraulic (keeper hole) that traps swimmers, kayakers, and rafters. Even experienced paddlers have drowned. ALWAYS portage around this structure — do not attempt to run it.
Part of the Great Falls hydroelectric complex; extremely powerful hydraulic; mandatory portage
📍 47.5204, -111.3011
⚠️ Hazard zone: 600 ft upstream + 500 ft downstream
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DANGER: Low-Head Dam — Morony Dam
Missouri River · MT
Hydraulic Recirculation Zone — Extremely Dangerous
Low-head dams create a submerged recirculating hydraulic (keeper hole) that traps swimmers, kayakers, and rafters. Even experienced paddlers have drowned. ALWAYS portage around this structure — do not attempt to run it.
Downstream of Great Falls hydroelectric run; floaters MUST portage; signage present but limited
📍 47.4780, -111.1850
⚠️ Hazard zone: 600 ft upstream + 500 ft downstream
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DANGER: Low-Head Dam — Yellowstone River Diversion at Billings
Yellowstone River · MT
Hydraulic Recirculation Zone — Extremely Dangerous
Low-head dams create a submerged recirculating hydraulic (keeper hole) that traps swimmers, kayakers, and rafters. Even experienced paddlers have drowned. ALWAYS portage around this structure — do not attempt to run it.
Irrigation diversion; spring runoff creates dangerous backroller
📍 45.7710, -108.5300
⚠️ Hazard zone: 500 ft upstream + 400 ft downstream
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DANGER: Low-Head Dam — Milltown Dam Site (Clark Fork)
Clark Fork River · MT
Hydraulic Recirculation Zone — Extremely Dangerous
Low-head dams create a submerged recirculating hydraulic (keeper hole) that traps swimmers, kayakers, and rafters. Even experienced paddlers have drowned. ALWAYS portage around this structure — do not attempt to run it.
Dam removed 2008 but concrete remnants create hydraulic at high water; marked hazard
📍 46.8785, -113.8820
⚠️ Hazard zone: 400 ft upstream + 300 ft downstream
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DANGER: Low-Head Dam — Flathead River Diversion at Polson
Flathead River · MT
Hydraulic Recirculation Zone — Extremely Dangerous
Low-head dams create a submerged recirculating hydraulic (keeper hole) that traps swimmers, kayakers, and rafters. Even experienced paddlers have drowned. ALWAYS portage around this structure — do not attempt to run it.
Below Flathead Lake outlet; high flows May–July from Hungry Horse releases
📍 47.6930, -114.1580
⚠️ Hazard zone: 450 ft upstream + 350 ft downstream
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Reservoir Levels & Access
Storage levels, boat ramp access, and downstream surge risk from BOR + USACE data.
Fort Peck Lake
Fort Peck Dam · Missouri River
❓ No data
fishingboatingcamping
Fourth-largest reservoir in US by volume. Releases affect downstream MO paddling.
📡 Downstream gauge: USGS 06115200
Live level data unavailable — BOR API
Hungry Horse Reservoir
Hungry Horse Dam · South Fork Flathead River
❓ No data
fishingboatingcamping
Near Glacier NP. Releases affect Flathead River levels and Clark Fork downstream.
📡 Downstream gauge: USGS 12355500
Live level data unavailable — BOR API
Canyon Ferry Lake
Canyon Ferry Dam · Missouri River (upper)
❓ No data
fishingboatingcamping
Helena area. Missouri River releases below affect paddling from below the dam to Great Falls.
📡 Downstream gauge: USGS 06054500
Live level data unavailable — BOR API
Bighorn Lake (Yellowtail Dam)
Yellowtail Dam · Bighorn River
❓ No data
fishingboatingcamping
Bighorn Canyon NRA. Tailwater downstream is world-class trophy trout fishery.
📡 Downstream gauge: USGS 06294000
Live level data unavailable — BOR API
📡 Data Sources
- Low-head dam database: USACE National Inventory of Dams (NID) + CO Dam Safety Branch + MT DNRC
- Reservoir levels: Bureau of Reclamation (BOR) RISE API — updated hourly
- Downstream flow: USGS National Water Information System — 30 min
- Surge warnings: Cross-reference BOR release data × USGS downstream gauges