Ryan-Tronrud Dam Reservoir Report

Last Updated: December 5, 2025

Ryan-Tronrud Dam, also known as Rein Lake, is a private-owned structure located in Sweet Grass, Montana.


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Summary

Built in 1956 by the USDA NRCS, this earth-type dam serves primarily for irrigation purposes along the TR-Sweetgrass Creek. With a height of 22 feet and a storage capacity of 800 acre-feet, it plays a crucial role in managing water resources in the area.

Situated in a picturesque location, the dam stands as a significant structure with a spillway width of 48 feet and a maximum discharge of 20 cubic feet per second. Despite being classified as having a significant hazard potential, the dam's condition assessment is currently not rated. It is regulated by the Montana Department of Natural Resources and Conservation, ensuring that it meets state inspection and enforcement standards.

As a key component of the local water management system, Ryan-Tronrud Dam represents a vital piece of infrastructure in ensuring water availability for agricultural activities in the region. With its historical significance and ongoing maintenance, the dam continues to play a crucial role in sustaining water resources and supporting the local community's irrigation needs.

Year Completed

1956

Dam Length

200

Dam Height

22

River Or Stream

TR-SWEETGRASS CREEK

Primary Dam Type

Earth

Hydraulic Height

19

Drainage Area

5

Nid Storage

800

Hazard Potential

Significant

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.