Diamond Lake Aeration Lagoon No 3 Reservoir Report

Last Updated: December 5, 2025

Diamond Lake Aeration Lagoon No 3 in Pend Oreille, Washington, is a public utility managed by the Washington Department of Ecology.


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Summary

This Earth-type dam, completed in 1987, has a hydraulic height of 17 feet and a structural height of 17 feet, with a storage capacity of 61 acre-feet. The lagoon covers an area of 51 acres and is located near the Tr-Little Spokane River-Offstr, within the jurisdiction of the state regulatory agency.

The dam is designed for purposes other than flood control or water supply, with a high hazard potential and a satisfactory condition assessment as of August 2021. The inspection frequency for the facility is every 5 years, and the last inspection was conducted in August 2021. The emergency action plan was last revised in July 1997, and additional risk assessment and management measures are not currently specified for the site.

Water resource and climate enthusiasts interested in the management and regulation of dams in Washington may find Diamond Lake Aeration Lagoon No 3 to be a compelling case study. With its unique design, storage capacity, and environmental context, this facility serves as a key point of interest for those studying water resources and infrastructure in the region.

Year Completed

1987

Dam Length

1570

River Or Stream

Tr-Little Spokane River-Offstr

Primary Dam Type

Earth

Surface Area

51

Hydraulic Height

17

Drainage Area

0.03

Nid Storage

61

Structural Height

17

Hazard Potential

High

Foundations

Rock, Soil

Nid Height

17
       
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.