Willow Lake Dam Reservoir Report
Last Updated: December 13, 2025
Willow Lake Dam, located in Freeport, Illinois, is a privately owned structure that serves multiple purposes, including recreation.
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Summary
Built in 1974 by designer JAMES F. GASTEL, this earth dam stands at a height of 25 feet and spans a length of 590 feet, with a storage capacity of 299 acre-feet. Situated on the Tributary of Pecatonica River, it plays a crucial role in regulating water flow and providing recreational opportunities for the community.
Managed by the Illinois Department of Natural Resources (IDNR), Willow Lake Dam has a spillway width of 55 feet and a maximum discharge capacity of 2313 cubic feet per second. With a hazard potential rated as high, the dam is inspected annually to ensure public safety. Despite its moderate risk assessment, the dam's condition assessment is currently not available, indicating a potential need for further evaluation and maintenance to mitigate any risks associated with its operation.
With its scenic location and vital role in water resource management, Willow Lake Dam stands as a significant landmark in Stephenson County, Illinois. As climate change continues to impact water resources, the proper maintenance and regulation of structures like Willow Lake Dam are essential to ensure the safety and sustainability of water systems in the region.
Year Completed |
1974 |
Dam Length |
590 |
Dam Height |
25 |
River Or Stream |
TRIB PECATONICA RIVER |
Primary Dam Type |
Earth |
Surface Area |
23 |
Drainage Area |
0.9 |
Nid Storage |
299 |
Outlet Gates |
Uncontrolled |
Hazard Potential |
High |
Foundations |
Unlisted/Unknown |
Nid Height |
25 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Pecatonica River At Freeport
|
733cfs |
Pecatonica River At Martintown
|
473cfs |
Sugar River Near Brodhead
|
342cfs |
Rock River At Byron
|
4300cfs |
Pecatonica River Nr Shirland
|
1300cfs |
Elkhorn Creek Near Penrose
|
44cfs |
Dam Data Reference
Condition Assessment
SatisfactoryNo 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
HighDams 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.
Willow Lake Dam