Henrys Lake Reservoir Report

Last Updated: December 5, 2025

Henrys Lake, also known as North Fork Reservoir, is a privately owned water resource located in Fremont County, Idaho.


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Summary

Managed by the Idaho Department of Water Resources, this reservoir on the Henrys Fork of the Snake River serves multiple purposes, including irrigation and wildlife habitat. Built in 1923, the dam stands at a height of 25.2 feet and has a storage capacity of 58,700 acre-feet.

With a surface area of 6,050 acres and a drainage area of 93.4 square miles, Henrys Lake plays a vital role in water management in the region. The dam's controlled spillway and slide gates ensure flood control and water release when needed. Despite its fair condition assessment and high hazard potential, the reservoir continues to be a valuable resource for the local community and wildlife.

In the event of an emergency, the reservoir has an Emergency Action Plan in place, though it has not been updated recently. With a very high risk assessment rating, it is crucial for stakeholders to ensure the proper management and maintenance of Henrys Lake to safeguard its surrounding areas and maintain its ecological balance.

Year Completed

1923

Dam Length

408

Dam Height

25.2

River Or Stream

HENRYS FORK SNAKE RIVER

Surface Area

6050

Hydraulic Height

22.5

Drainage Area

93.4

Nid Storage

58700

Outlet Gates

Slide (sluice gate)

Hazard Potential

High

Foundations

Rock, Soil

Nid Height

25
       
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.