Rainbow Springs Dam Reservoir Report

Last Updated: December 15, 2025

Rainbow Springs Dam, located in Snohomish, Washington, stands as a testament to human ingenuity and the harmonious intersection of water resource management and recreational activities.


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Summary

Built in 1969, this private-owned earth dam on the Tr-South Fork Stillaguamish River boasts a structural height of 12 feet and a hydraulic height of 14 feet, providing a maximum storage capacity of 63 acre-feet for the surrounding area. Despite its impressive stature, the dam's condition assessment reveals a poor rating, with a high hazard potential, highlighting the importance of regular inspections and maintenance to ensure its continued safety and functionality.

The primary purpose of Rainbow Springs Dam is recreation, offering visitors a tranquil retreat in the midst of nature's beauty. With a normal storage capacity of 43 acre-feet and a surface area of 43 acres, the dam provides a serene setting for fishing, boating, and other water-based activities. However, the dam's last inspection in September 2018 raised concerns about its structural integrity, underscoring the need for ongoing monitoring and potential rehabilitation efforts to address any safety risks associated with its aging infrastructure.

Managed by the Washington Department of Ecology, Rainbow Springs Dam falls under state jurisdiction and regulation, with permitting, inspection, and enforcement processes in place to ensure compliance with safety standards and environmental protection measures. As climate change continues to impact water resources and infrastructure resilience, the importance of maintaining and updating dams like Rainbow Springs becomes increasingly vital in safeguarding communities and ecosystems against potential hazards and ensuring sustainable water management for future generations.

Year Completed

1969

Dam Length

900

River Or Stream

Tr-South Fork Stillaguamish

Primary Dam Type

Earth

Surface Area

43

Hydraulic Height

14

Drainage Area

0.56

Nid Storage

63

Structural Height

12

Hazard Potential

High

Foundations

Unlisted/Unknown

Nid Height

14
       
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.