May Lake Dam Reservoir Report

Last Updated: December 13, 2025

May Lake Dam, located in Stevens County, Washington, is a privately owned structure that serves primarily for irrigation purposes.


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Summary

Completed in 1950, this earth dam stands at a structural height of 12 feet and has a hydraulic height of the same measure. With a normal storage capacity of 11 acre-feet and a maximum storage of 15 acre-feet, the dam covers a surface area of 4.2 acres and has a drainage area of 0.7 square miles, making it a crucial resource for water management in the region.

Managed by the Washington Department of Ecology, May Lake Dam is subject to state regulation, inspection, and enforcement to ensure its safety and compliance with water resource management guidelines. Despite being classified as having a high hazard potential, the dam is currently in fair condition as of the latest assessment in August 2021. With a scheduled inspection frequency of every five years, the dam's emergency action plan is being continuously updated to meet safety guidelines and address any potential risks associated with its operation.

Situated on Tr-Mill Creek, May Lake Dam plays a vital role in supporting local irrigation needs and providing opportunities for recreational activities. With its strategic location and significant contribution to water storage and management, the dam stands as a key infrastructure for both water resource enthusiasts and climate advocates in the region.

Year Completed

1950

Dam Length

254

River Or Stream

Tr-Mill Creek

Primary Dam Type

Earth

Surface Area

4.2

Hydraulic Height

12

Drainage Area

0.7

Nid Storage

15

Structural Height

12

Hazard Potential

High

Foundations

Soil

Nid Height

12
       
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.