Sinlahekin Dam No 1 Reservoir Report

Last Updated: December 15, 2025

Sinlahekin Dam No 1, also known as Forde Lake, is a state-owned earth dam located in Loomis, Washington.


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Summary

Completed in 1949, this dam serves primarily for recreational purposes, offering a serene setting for outdoor enthusiasts to enjoy activities such as fishing and boating. Situated on Sinlahekin Creek, the dam has a hydraulic height of 14 feet and a structural height of 12 feet, with a storage capacity of 333 acre-feet and a surface area of 83 acres.

Managed by the Washington Department of Ecology, Sinlahekin Dam No 1 has a high hazard potential but is currently in satisfactory condition. With its stone core and rock-soil foundations, the dam supports the surrounding ecosystem while providing essential water resources for the region. Its proximity to the Okanogan National Forest offers visitors a chance to connect with nature and appreciate the importance of preserving our water sources in the face of climate change.

As a vital infrastructure in Okanogan County, Sinlahekin Dam No 1 undergoes regular inspections to ensure its safety and functionality. With its location in a picturesque landscape and its role in supporting recreational activities, this dam serves as a reminder of the delicate balance between water resource management and environmental conservation. For water resource and climate enthusiasts, Sinlahekin Dam No 1 is a symbol of the ongoing efforts to protect and sustainably utilize our precious natural resources.

Year Completed

1949

Dam Length

180

River Or Stream

Sinlahekin Creek

Primary Dam Type

Earth

Surface Area

83

Hydraulic Height

14

Drainage Area

64

Nid Storage

333

Structural Height

12

Hazard Potential

High

Foundations

Rock, Soil

Nid Height

14
       
Seasonal Comparison

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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.