Mavis Pond #1 Dam Reservoir Report

Last Updated: December 5, 2025

Mavis Pond #1 Dam, located in Thompson, Connecticut, was completed in 1870 and serves as a recreational spot with a primary purpose of providing leisure activities for visitors.


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Summary

The dam, standing at a height of 13 feet and a length of 172 feet, has a storage capacity of 65 acre-feet and is situated on the Fivemile River within the Windham County. The structure is classified as a Masonry dam and is regulated by the Connecticut Department of Energy and Environmental Protection (DEEP).

With a significant hazard potential, Mavis Pond #1 Dam is not currently rated for its condition assessment and lacks an Emergency Action Plan (EAP). Despite these gaps, the dam continues to be a popular spot for outdoor enthusiasts looking to enjoy the scenic surroundings and recreational opportunities it provides. The dam has a spillway width of 12 feet and a maximum discharge capacity of 32 cubic feet per second, ensuring proper water flow management in case of high water levels.

While Mavis Pond #1 Dam has not been modified in recent years and lacks some key safety measures, its role in providing recreational activities and its historical significance make it an important landmark in the area. With its location along the Fivemile River and its proximity to Thompson, the dam remains a notable feature for water resource and climate enthusiasts looking to explore the diverse landscapes of Connecticut.

Year Completed

1870

Dam Length

172

Dam Height

13

River Or Stream

FIVEMILE RIVER

Primary Dam Type

Masonry

Surface Area

12

Drainage Area

2.82

Nid Storage

65

Hazard Potential

Significant

Nid Height

13
       
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.