Little Spider Lake Reservoir Report

Last Updated: December 5, 2025

Little Spider Lake, located in Iron River, Wisconsin, is a picturesque reservoir created by the Mullenhoff Dam in 1929.


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Summary

This private dam stands at a height of 7 feet and has a total length of 400 feet, with a normal storage capacity of 200 acre-feet. The dam serves as the outlet for Mullenhoff Lake, contributing to a surface area of 69 acres and a drainage area of 0.8 square miles.

Despite its age, the Little Spider Lake dam has a low hazard potential and is currently rated as "Not Rated" in terms of condition assessment. While the dam is regulated by the Wisconsin Department of Natural Resources and subject to inspection and enforcement measures, it has not been evaluated for its emergency action plan or risk management measures. With a maximum discharge capacity of 20 cubic feet per second and an uncontrolled spillway type, the reservoir presents a moderate risk level but remains a captivating site for water resource and climate enthusiasts in Bayfield County.

As a focal point for outdoor enthusiasts and environmentalists, Little Spider Lake offers a unique blend of natural beauty and historical significance. From its scenic surroundings to its engineering marvels, this reservoir continues to serve as a vital water resource in Wisconsin, inviting visitors to explore its tranquil waters and appreciate the delicate balance between human intervention and environmental preservation.

Year Completed

1929

Dam Length

400

Dam Height

7

River Or Stream

OUTLET OF MULLENHOFF LAKE

Primary Dam Type

Earth

Surface Area

69

Hydraulic Height

3

Drainage Area

0.8

Nid Storage

270

Structural Height

7

Hazard Potential

Low

Nid Height

7
       
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.