Johnson Mill Pond Dam Reservoir Report

Last Updated: December 5, 2025

Johnson Mill Pond Dam, located in East Haddam, Connecticut, is a privately owned structure on the Moodus River that serves primarily for recreational purposes.


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Summary

Built in 1880, the dam stands at a height of 24.9 feet and has a storage capacity of 143 acre-feet. With a drainage area of 15.7 square miles, the dam has a maximum discharge of 2544 cubic feet per second and a surface area of 13.9 acres.

This significant dam has been inspected regularly, with the last inspection conducted in December 2017, revealing a satisfactory condition. Despite its age, the structure has been well-maintained, meeting state regulations and enforcement requirements. However, its hazard potential is considered significant, necessitating emergency action preparedness. The dam has no associated locks or spillways, emphasizing its reliance on its design and structural integrity for effective water management in the region.

For water resource and climate enthusiasts, Johnson Mill Pond Dam presents an intriguing case study of a historic earth dam that continues to play a vital role in local water management and recreational activities. Its location on the Moodus River adds to its ecological significance, highlighting the intersection of human infrastructure with natural waterways. As efforts to monitor and maintain the dam persist, its resilience in the face of changing climate conditions will be a key area of interest for those invested in sustainable water resource management.

Year Completed

1880

Dam Length

414.5

Dam Height

24.9

River Or Stream

MOODUS RIVER

Primary Dam Type

Earth

Surface Area

13.9

Drainage Area

15.7

Nid Storage

143

Hazard Potential

Significant

Nid Height

25
       
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