Grasmere Middle Dam Reservoir Report
Nearby: Grasmere North Dam Grasmere East Dam
Last Updated: January 11, 2026
Grasmere Middle Dam, also known as Grasmere Reservoir North Middle Dam, is a privately owned structure located in Owyhee, Idaho.
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Summary
Completed in 1936, this earth dam stands at a height of 15.5 feet and has a hydraulic height of 12.2 feet. It plays a crucial role in water resource management, with a storage capacity of 420.2 acre-feet and a surface area of 152.9 acres.
Situated on Rattlesnake Creek and Marys Creek, Grasmere Middle Dam serves various purposes beyond water storage. Despite its poor condition assessment and low hazard potential, the dam is deemed to have a moderate risk level. With a drainage area of 1.3 square miles and a maximum discharge rate of 18 cubic feet per second, this structure is subject to state regulation, inspection, and enforcement by the Idaho Department of Water Resources.
While Grasmere Middle Dam does not have a federal owner or funding, its presence is essential for maintaining water resources in the region. The dam's uncontrolled spillway, lack of outlet gates, and poor condition warrant attention for potential risk management measures. For water resource and climate enthusiasts, understanding the role and condition of Grasmere Middle Dam is vital for ensuring the safety and sustainability of the surrounding communities and ecosystems.
Year Completed |
1936 |
Dam Length |
700 |
Dam Height |
15.5 |
River Or Stream |
RATTLESNAKE CREEK MARYS CREEK |
Surface Area |
152.9 |
Hydraulic Height |
12.2 |
Drainage Area |
1.3 |
Nid Storage |
420.2 |
Outlet Gates |
None |
Hazard Potential |
Low |
Foundations |
Rock, Soil |
Nid Height |
16 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Dam Data Reference
Condition Assessment
SatisfactoryNo 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
HighDams 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.
Grasmere Middle Dam
Duncan Creek