Square Lake Dam Reservoir Report

Last Updated: December 16, 2025

Square Lake Dam, located in Leavenworth, Washington, is a crucial part of the region's water management infrastructure.


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Summary

Built in 1938 for irrigation purposes, this rockfill dam on Prospect Creek stands at a structural height of 7 feet and has a storage capacity of 913 acre-feet. With a surface area of 500 acres and a drainage area of 1.2 square miles, the dam plays a vital role in regulating water flow and storage for agricultural use in the surrounding area.

Despite its importance, Square Lake Dam has been deemed to have a high hazard potential and poor condition assessment, requiring frequent inspections and maintenance. The last inspection in August 2018 highlighted the need for improvements to ensure the safety and functionality of the dam. Managed by a public utility, the dam is under the jurisdiction of the Washington Department of Ecology, which oversees its regulation, permitting, inspection, and enforcement to ensure compliance with state standards and guidelines.

As climate change continues to impact water resources, the maintenance and management of dams like Square Lake Dam become increasingly critical. With its historical significance and continued importance for irrigation and recreation, ensuring the safety and efficiency of Square Lake Dam is essential for water resource and climate enthusiasts alike.

Year Completed

1938

Dam Length

104

River Or Stream

Prospect Creek

Primary Dam Type

Rockfill

Surface Area

500

Hydraulic Height

7

Drainage Area

1.2

Nid Storage

913

Structural Height

7

Hazard Potential

High

Foundations

Rock, Soil

Nid Height

7
       
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.