Sheridan Reservoir Report

Last Updated: December 5, 2025

Sheridan is a privately owned dam located in Island Park Reservoir, Idaho, along the East Fork Big Lost River and Big Lost River.


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Summary

Built in 1873, this earth dam stands at 22.4 meters high with a hydraulic height of 18.4 meters. With a storage capacity of 2105 acre-feet and a surface area of 286 acres, Sheridan plays a crucial role in water resource management in the region.

Despite its historical significance, Sheridan faces significant risk due to its poor condition assessment and the potential for significant hazards. With a very high risk rating, this dam requires immediate attention and maintenance to ensure its structural integrity and the safety of surrounding communities. The dam features a controlled spillway type with slide gates for water release, but there are no locks associated with the structure.

It is essential for water resource and climate enthusiasts to monitor the condition of Sheridan closely, as its poor state and high risk rating pose a threat to the local ecosystem and water supply. With state regulations, permitting, inspection, and enforcement in place, efforts must be made to address the dam's maintenance needs and ensure its long-term sustainability. A collaborative approach involving various agencies and stakeholders is necessary to protect this vital water resource in the Idaho region.

Year Completed

1873

Dam Length

2340

Dam Height

22.4

River Or Stream

EAST FORK BIG LOST RIVER BIG LOST RIVER

Surface Area

286

Hydraulic Height

18.4

Drainage Area

7.3

Nid Storage

2105

Outlet Gates

Slide (sluice gate)

Hazard Potential

Significant

Foundations

Rock, Soil

Nid Height

22
       
Seasonal Comparison

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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.