The Tarn Reservoir Report

Last Updated: December 20, 2025

Nestled in the beautiful Hancock County, Maine, The Tarn is a recreational dam that stands as a testament to early 20th-century engineering.


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Summary

Completed in 1900, this Federal-owned structure on Cromwell Brook offers visitors a serene escape with its 165-acre normal storage capacity and 20-acre surface area. With a dam height of 7 feet and a hydraulic height of 6 feet, The Tarn provides a low-hazard recreational oasis for enthusiasts of water resources and climate.

Managed by the Maine Emergency Management Agency (MEMA) and regulated by the state, The Tarn's condition is currently not rated, with its last inspection dating back to October 2010. Despite its age, this dam continues to serve its primary purpose of recreation, offering a tranquil setting for outdoor activities. The Tarn's location, just a stone's throw from the charming town of Hancock, makes it a popular destination for locals and visitors alike.

With its rich history and picturesque surroundings, The Tarn stands as a symbol of Maine's commitment to preserving its natural resources. As climate enthusiasts explore the region, they can appreciate the careful maintenance and management of this Federal-owned structure, ensuring its continued safety and enjoyment for generations to come.

Year Completed

1900

Dam Length

19

Dam Height

7

River Or Stream

Cromwell Brook

Primary Dam Type

Other

Surface Area

20

Hydraulic Height

6

Nid Storage

184

Structural Height

7

Hazard Potential

Low

Nid Height

7
       
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.