Lake Ellis Dam Reservoir Report

Last Updated: December 11, 2025

Lake Ellis Dam in Athol, Massachusetts, is a significant earth dam with a primary purpose of recreation.


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Summary

Built in 1852, the dam stands at a height of 13.2 feet and has a hydraulic height of 5.5 feet, creating a reservoir with a storage capacity of 1115 acre-feet. The dam is situated on the Mill Brook River and is regulated by the Department of Conservation and Recreation in Massachusetts.

With a fair condition assessment and a significant hazard potential, Lake Ellis Dam is subject to regular inspections every five years. Despite its age, the dam continues to serve its intended purpose of providing recreational opportunities for the local community. The dam has a surface area of 66 acres and a normal storage capacity of 310 acre-feet, making it a valuable resource for water recreation enthusiasts in the region.

Although the dam does not have a spillway, its risk assessment is considered high, highlighting the importance of ongoing risk management measures. The dam's location in Worcester County, Massachusetts, makes it a key feature in the local landscape and a vital component of the region's water resource infrastructure. For water resource and climate enthusiasts, Lake Ellis Dam represents both a historic landmark and a vital piece of infrastructure in the ongoing management of water resources in the area.

Year Completed

1852

Dam Length

210

Dam Height

13.2

River Or Stream

MILL BROOK RIVER

Primary Dam Type

Earth

Surface Area

66

Hydraulic Height

5.5

Drainage Area

3.7

Nid Storage

1115

Hazard Potential

Significant

Foundations

Unlisted/Unknown

Nid Height

13
       
Seasonal Comparison

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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.