Cascade Lake Dam Reservoir Report

Last Updated: December 13, 2025

Cascade Lake Dam, located in Rosario, Washington, is a privately owned structure with a primary purpose of water supply.


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Summary

Built in 1915, this Arch type dam stands at a hydraulic height of 21 feet, with a structural height of 17 feet. It holds a normal storage capacity of 1700 acre-feet and has a maximum storage capacity of 2670 acre-feet, serving as a vital resource for the surrounding area.

The dam also serves secondary purposes such as hydroelectric power generation and recreation, adding to its significance in the region. With a hazard potential classified as high, the dam's condition assessment is rated as fair. Regular inspections, last conducted in June 2018, ensure its safety and structural integrity. The Washington Department of Ecology oversees the regulatory aspects of the dam, including permitting, inspection, and enforcement, highlighting the importance of government oversight in water resource management.

With its location on Tr-Cascade Bay and its close proximity to the San Juan Islands, Cascade Lake Dam plays a crucial role in the water supply infrastructure of San Juan County. Its historical significance, combined with its multiple functions and regulatory oversight, make it a key feature for water resource and climate enthusiasts to study and appreciate in the Pacific Northwest region.

Year Completed

1915

River Or Stream

Tr-Cascade Bay

Primary Dam Type

Arch

Surface Area

170

Hydraulic Height

21

Drainage Area

3.42

Nid Storage

2670

Structural Height

17

Hazard Potential

High

Foundations

Soil

Nid Height

21
       
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.