Happy Hollow Lake Dam Reservoir Report
Last Updated: December 14, 2025
Happy Hollow Lake Dam, located in Dahinda, Illinois, along the tributary of Spoon River, is a private-owned structure with a primary purpose of recreation.
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Summary
Built in 1940 by JACOB A. HARMAN, this earth dam stands at a height of 52 feet and has a length of 260 feet, providing a storage capacity of 232 acre-feet. The dam is regulated by the Illinois Department of Natural Resources (IDNR) and undergoes regular inspections and enforcement to ensure its safety and compliance.
With a hazard potential rated as significant and a moderate risk assessment, Happy Hollow Lake Dam is a crucial structure in the region. The dam features uncontrolled spillway and outlet gates and is designed to withstand the demands of recreational activities while ensuring the safety of nearby communities. Despite its age, the dam has not had a condition assessment available, but it is inspected every three years to maintain its structural integrity and mitigate any potential risks.
For water resource and climate enthusiasts, Happy Hollow Lake Dam serves as a fascinating case study in dam management and regulation. Its location in Knox County, Illinois, highlights the importance of private ownership in maintaining recreational water resources. As climate change continues to impact water infrastructure, the management of dams like Happy Hollow Lake Dam becomes increasingly vital to ensure the safety and sustainability of water resources for future generations.
Year Completed |
1940 |
Dam Length |
260 |
Dam Height |
52 |
River Or Stream |
TRIB SPOON RIVER |
Primary Dam Type |
Earth |
Nid Storage |
232 |
Outlet Gates |
Uncontrolled |
Hazard Potential |
Significant |
Foundations |
Unlisted/Unknown |
Nid Height |
52 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
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.
Happy Hollow Lake Dam