Holter Dam Reservoir Report

Last Updated: December 5, 2025

Holter Dam, located on the Missouri River in Montana, is a gravity dam with a height of 124 feet and a length of 1364 feet.


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Summary

Completed in 1918, this dam serves multiple purposes, including flood risk reduction and hydroelectric power generation. With a normal storage capacity of 245,000 acre-feet and a maximum storage of 306,000 acre-feet, Holter Dam plays a crucial role in managing water resources in the region.

The dam is owned by a private entity and regulated by the Federal Energy Regulatory Commission. With a high hazard potential and a very high risk assessment rating, the safety and management of Holter Dam are of utmost importance. The spillway, with a width of 558 feet, is controlled, and the dam features outlet gates for water release. Despite its age, the dam's condition assessment is not available, highlighting the need for regular inspections and risk management measures.

Holter Dam's location in Lewis and Clark County, Montana, makes it a significant structure in the region's water resource infrastructure. The dam has a controlled spillway and a high hydraulic height of 120 feet, contributing to its flood risk reduction capabilities. As a key hydroelectric facility in the area, the dam provides clean energy while also ensuring water security and flood control for the surrounding communities.

Year Completed

1918

Dam Length

1364

Dam Height

124

River Or Stream

Missouri River

Primary Dam Type

Gravity

Surface Area

4550

Hydraulic Height

120

Drainage Area

17150

Nid Storage

306000

Structural Height

124

Outlet Gates

Other Controlled - 21, Slide (sluice gate) - 10

Hazard Potential

High

Nid Height

124
       
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.