Grass Lake Dam Reservoir Report

Last Updated: December 5, 2025

Grass Lake Dam, located in Benzie County, Michigan, is a gravity dam on the Betsie River that was completed in 1951 for recreational purposes.


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Summary

With a height of 8.4 feet and a hydraulic height of 5.4 feet, the dam has a storage capacity of 5200 acre-feet and a normal storage level of 675 acre-feet. The dam spans 176 feet in length and covers a surface area of 482 acres, serving as a popular spot for outdoor enthusiasts in the Wallin area.

Despite being categorized as having a low hazard potential and a satisfactory condition assessment as of 2014, the dam is subject to moderate risk (3) due to its location and structure. The spillway, with a width of 62 feet, is uncontrolled, allowing for a maximum discharge of 1600 cubic feet per second. The dam is not regulated by the state and has not been inspected or permitted by state agencies, indicating a lack of oversight in its maintenance and operation.

Given its historical significance and recreational value, Grass Lake Dam serves as both a landmark and a potential area of concern for water resource and climate enthusiasts. Its location on the Betsie River and the surrounding Benzie County landscape make it a critical piece of infrastructure to monitor and maintain to ensure the safety and sustainability of the local ecosystem and community.

Year Completed

1951

Dam Length

176

Dam Height

8.4

River Or Stream

Betsie River

Primary Dam Type

Gravity

Surface Area

482

Hydraulic Height

5.4

Drainage Area

77.9

Nid Storage

5200

Structural Height

8.4

Hazard Potential

Low

Nid Height

8
       
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.