Johnstown Reservoir Report

Last Updated: December 5, 2025

Johnstown, located in Weld County, Colorado, is home to a critical water resource infrastructure known as the Johnstown Dam.


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Summary

Completed in 1953, this earth dam on the Big Thompson River-OS serves as a vital water supply source for the region, with a storage capacity of 350 acre-feet and a surface area of 34 acres. Despite its importance, the dam's condition assessment in 2020 deemed it unsatisfactory, with a high hazard potential, indicating the need for significant maintenance and upgrades to ensure the safety of the surrounding community.

The Johnstown Dam, standing at 16 feet in height and stretching over 5737 feet in length, plays a crucial role in water management and supply for the area. However, its high risk assessment of 2 (on a scale of 1-5) underscores the urgency of addressing its structural integrity and hazard potential. With state regulation and inspection in place, efforts must be intensified to improve the dam's condition and reduce the risk to downstream communities in case of a potential failure.

As water resource and climate enthusiasts, the situation at the Johnstown Dam highlights the importance of proactive maintenance and risk management for critical infrastructure in the face of changing environmental conditions. It serves as a reminder of the ongoing challenges faced in safeguarding our water resources and infrastructure against potential threats, underscoring the need for continued monitoring, investment, and community engagement to ensure resilience in the face of a changing climate.

Year Completed

1953

Dam Length

5737

Dam Height

13

River Or Stream

BIG THOMPSON RIVER-OS

Primary Dam Type

Earth

Surface Area

34

Hydraulic Height

13

Nid Storage

350

Structural Height

16

Hazard Potential

High

Nid Height

16
       
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.