Long Lake Reservoir Report

Last Updated: December 5, 2025

Long Lake, located in Hoffman, Minnesota, is a state-regulated water resource managed by the Minnesota Department of Natural Resources.


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Summary

This reservoir on the Chippewa River was completed in 1938 and serves various purposes, with a primary dam type of "Other" and a buttress core type. The dam stands at a height of 6 feet and has a hydraulic height of 1.9 feet, with a storage capacity of 2255 acre-feet and a surface area of 218 acres.

With a drainage area of 143 square miles, Long Lake has a low hazard potential and is in satisfactory condition according to a 2009 assessment. The reservoir has a normal storage capacity of 1640 acre-feet and a maximum discharge of 1470 cubic feet per second. Despite being unlisted for spillway type and having no associated locks, Long Lake provides valuable water resources for the region and is subject to state inspection, permitting, and enforcement to ensure its safety and efficiency for water and climate enthusiasts.

Year Completed

1938

Dam Length

35

Dam Height

6

River Or Stream

CHIPPEWA RIVER

Primary Dam Type

Other

Surface Area

218

Hydraulic Height

1.9

Drainage Area

143

Nid Storage

2255

Structural Height

8

Hazard Potential

Low

Foundations

Unlisted/Unknown

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.