Diablo Reservoir Near Newhalem Reservoir Report

Nearby: Ross Gorge

Last Updated: December 29, 2025

Diablo Reservoir is a man-made lake located near Newhalem, WA in the North Cascades.


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Summary

The reservoir was created in 1930 to generate hydroelectric power for the city of Seattle. The hydrology of the lake is heavily influenced by the Skagit River, which feeds into the lake. Specific surface flow comes from the Skagit River, as well as several smaller creeks and streams in the area. The reservoir is also a major provider of snowpack, which is critical for maintaining water levels during the dry summer months. The water from Diablo Reservoir is primarily used for hydroelectric power generation, but it also supports local agriculture and recreational activities such as fishing, boating, and camping. The surrounding wilderness is home to a variety of wildlife, including bears, mountain goats, and bald eagles.

Reservoir Details

Lake Or Reservoir Water Surface Elevation Above Ngvd 1929, Ft 24hr Change -0.03%
Percent of Normal 100%
Minimum 1,193.5 ft
2017-09-11
Maximum 1,204.8 ft
2009-11-21
Average 1,201 ft
Dam_Height 389
Hydraulic_Height 335
Drainage_Area 1160
Year_Completed 1929
Nid_Storage 89200
Structural_Height 389
Foundations Rock
Surface_Area 770
Outlet_Gates Tainter (radial) - 19
River_Or_Stream Skagit River
Dam_Length 1180
Hazard_Potential High
Primary_Dam_Type Concrete
Nid_Height 389
       
Seasonal Comparison
Lake Or Reservoir Water Surface Elevation Above Ngvd 1929, Ft Levels

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.