Twin Lakes South Reservoir Report

Last Updated: December 6, 2025

Twin Lakes South is a privately owned irrigation dam located in Bear River Confluence, Idaho.


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Summary

Built in 1920, this earth dam stands at a height of 35.5 feet and has a hydraulic height of 31 feet, with a storage capacity of 14,000 acre-feet. Despite its age, the dam's condition is assessed as satisfactory, with a high hazard potential due to its location near the Deep Creek and Bear River.

The dam does not have a spillway, and water is controlled through slide gates. The last inspection in November 2020 deemed the structure to be in good condition. However, due to its high-risk potential, it is crucial for regulatory agencies like IDWR to continue regular inspections and maintenance to ensure the safety of surrounding communities and the integrity of the dam. Twin Lakes South serves a vital purpose in irrigation, making it a key water resource in the area.

With its historical significance and essential role in water management, Twin Lakes South highlights the intersection of water resource management and climate resilience. As climate change poses increasing challenges to water availability and infrastructure safety, the proper regulation and maintenance of dams like Twin Lakes South become even more critical. By staying vigilant in monitoring and addressing potential risks, stakeholders can ensure the continued functionality and safety of this important irrigation structure for years to come.

Year Completed

1920

Dam Length

930

Dam Height

35.5

River Or Stream

DEEP CREEK BEAR RIVER

Surface Area

493

Hydraulic Height

31

Drainage Area

2.2

Nid Storage

14000

Outlet Gates

Slide (sluice gate)

Hazard Potential

High

Foundations

Rock, Soil

Nid Height

36
       
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.