Lake Isabelle Reservoir Report

Last Updated: December 4, 2025

Lake Isabelle, located in Boulder, Colorado, is a privately owned reservoir with a primary purpose of irrigation.


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Summary

Built in 1925, this rockfill dam stands at a height of 38 feet and has a storage capacity of 738 acre-feet. The reservoir covers an area of 36 acres and is fed by the S F St Vrain Creek.

Despite its age, Lake Isabelle has a low hazard potential and its condition is currently not rated. The last inspection of the dam was conducted in 1990, but there have been no recent assessments. The risk assessment for the dam is classified as high, with a risk level of 2, although specific risk management measures are not detailed in the data provided.

Overall, Lake Isabelle serves as a vital water resource for irrigation purposes in the region, with a significant storage capacity and a history dating back to the early 20th century. Climate and water resource enthusiasts may find this reservoir intriguing due to its historical significance and role in supporting agricultural activities in the area.

Year Completed

1925

Dam Height

38

River Or Stream

S F ST VRAIN CREEK

Primary Dam Type

Rockfill

Surface Area

36

Hydraulic Height

38

Drainage Area

2

Nid Storage

738

Structural Height

38

Hazard Potential

Low

Nid Height

38
       
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.
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Area Campgrounds