Olson Lake Dam is an earth dam located in Winnebago County, Illinois, built in 1991. It carries a Low hazard potential classification.
Dam profile
NID height · 24 ft24 ft tall and 1,130 ft long. Height is drawn to scale against a two-story house, about 25 ft; the profile is a generic embankment section and the water level is illustrative.
About Olson Lake Dam
The primary purpose of Olson Lake Dam is recreation. The dam creates a reservoir used for recreational activities such as fishing, boating, and swimming. The dam is owned by Illinois Department of Natural Resources (state). It impounds the Willow Creek near Argyle.
The dam stands 24 feet tall and stretches 1,130 feet across, creates a reservoir covering 12 acres, has a maximum storage capacity of 630 acre-feet, and collects water from a drainage area of 9 square miles. Completed in 1991, the structure is 35 years old.
This dam has a low hazard potential classification, meaning that failure would cause minimal damage, limited primarily to the dam owner's property, with no expected loss of life. The most recent inspection on record was 07/23/2025.
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Location
| State | Illinois |
| County | Winnebago |
| Nearest City | Argyle |
| River/Stream | Willow Creek |
| Coordinates | 42.35347, -88.96268 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 24 ft |
| Dam Height | 24 ft |
| Dam Length | 1,130 ft |
| Year Completed | 1991 (35 years old) |
Storage & Hydraulics
| NID Storage | 630 acre-ft |
| Max Storage | 630 acre-ft |
| Normal Storage | 218 acre-ft |
| Surface Area | 12 acres |
| Drainage Area | 9 sq mi |
| Max Discharge | 4,588 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Recreation |
| Owner | Illinois Department of Natural Resources |
| Owner Type | State |
| Hazard Classification | Low |
| Condition Assessment | Not assessed |
| Last Inspection | 07/23/2025 |
| Emergency Action Plan | No |
Identifiers
| NID ID | IL50236 |
| Federal ID | IL50236 |
| More Info | State Dam Safety Program |