Green Mountain Reservoir Report

Last Updated: December 5, 2025

Green Mountain, located in Summit County, Colorado, is a federal-owned dam managed by the Bureau of Reclamation for hydroelectric power generation, irrigation, and recreation purposes.


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Summary

Completed in 1942, this Earth dam stands at 309 feet tall and spans 1150 feet across the Blue River, with a storage capacity of 161,850 acre-feet and a surface area of 2125 acres. The dam's spillway, controlled by slide and valve gates, has a width of 75 feet, and the maximum discharge capacity is 27,000 cubic feet per second.

With a high hazard potential and a very high risk assessment rating, Green Mountain is closely regulated and inspected by the Bureau of Reclamation to ensure its structural integrity and the safety of downstream communities. The dam's emergency action plan was last revised in January 2020, and although the condition assessment is not available, regular inspections are conducted to monitor its performance. Despite being a critical piece of infrastructure, the dam poses a potential risk due to its age and the surrounding environment, emphasizing the importance of ongoing risk management measures to mitigate any potential hazards.

Year Completed

1942

Dam Length

1150

Dam Height

309

River Or Stream

BLUE RIVER

Primary Dam Type

Earth

Surface Area

2125

Hydraulic Height

258

Drainage Area

599

Nid Storage

161850

Structural Height

309

Outlet Gates

Slide (sluice gate) - 2, Valve - 2

Hazard Potential

High

Foundations

Rock, Soil

Nid Height

309
       
Seasonal Comparison

Weather Forecast

Dam Data Reference

Condition Assessment

Satisfactory
No existing or potential dam safety deficiencies are recognized. Acceptable performance is expected under all loading conditions (static, hydrologic, seismic) in accordance with the minimum applicable state or federal regulatory criteria or tolerable risk guidelines.
Fair
No existing dam safety deficiencies are recognized for normal operating conditions. Rare or extreme hydrologic and/or seismic events may result in a dam safety deficiency. Risk may be in the range to take further action. Note: Rare or extreme event is defined by the regulatory agency based on their minimum
Poor A dam safety deficiency is recognized for normal operating conditions which may realistically occur. Remedial action is necessary. POOR may also be used when uncertainties exist as to critical analysis parameters which identify a potential dam safety deficiency. Investigations and studies are necessary.
Unsatisfactory
A dam safety deficiency is recognized that requires immediate or emergency remedial action for problem resolution.
Not Rated
The dam has not been inspected, is not under state or federal jurisdiction, or has been inspected but, for whatever reason, has not been rated.
Not Available
Dams for which the condition assessment is restricted to approved government users.

Hazard Potential Classification

High
Dams assigned the high hazard potential classification are those where failure or mis-operation will probably cause loss of human life.
Significant
Dams assigned the significant hazard potential classification are those dams where failure or mis-operation results in no probable loss of human life but can cause economic loss, environment damage, disruption of lifeline facilities, or impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be in areas with population and significant infrastructure.
Low
Dams assigned the low hazard potential classification are those where failure or mis-operation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.
Undetermined
Dams for which a downstream hazard potential has not been designated or is not provided.
Not Available
Dams for which the downstream hazard potential is restricted to approved government users.