Dillon Reservoir Reservoir Report

Last Updated: December 5, 2025

Dillon Reservoir, also known as Lake Dillon, is a man-made reservoir located in Summit County, Colorado.


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Summary

The reservoir was created in 1963 after the construction of the Dillon Dam on the Blue River. The hydrology of the reservoir is mainly fed by the Blue River and its tributaries, as well as snowmelt from the surrounding mountain ranges. The surface flow of the reservoir is regulated by the Denver Water Board, which operates the dam. The snowpack providers for the reservoir are the surrounding mountains, which receive heavy snowfall during the winter months. The water stored in the reservoir is mainly used for municipal purposes, such as drinking water for the Denver metro area. However, the reservoir also supports agricultural irrigation and recreational activities, including boating, fishing, and camping.

Reservoir Details

Storage 24hr Change -0.08%
Percent of Normal 89%
Minimum 120,377.0 acre-ft
2003-03-17
Maximum 264,121.156 acre-ft
2009-06-03
Average 229,726 acre-ft
Nid_Height 310
Hydraulic_Height 231
Primary_Dam_Type Earth
Drainage_Area 338
Years_Modified 1986 - Hydraulic, 1986 - Mechanical, 2002 - Hydraulic, 2002 - Mechanical
Year_Completed 1963
Dam_Height 231
Structural_Height 310
River_Or_Stream BLUE RIVER
Foundations Rock, Soil
Surface_Area 3300
Hazard_Potential High
Outlet_Gates Slide (sluice gate) - 4, Valve - 5
Nid_Storage 305000
Dam_Length 5900
       
Seasonal Comparison
Storage Levels
Storage Levels
Pool Elevation Levels
Total Release Levels
Inflow 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.