Alton Twin Lakes-south Lake Dam is an earth dam located in Madison County, Illinois, built in 1970. It carries a Significant hazard potential classification.
Dam profile
NID height · 32 ft32 ft tall and 300 ft long, taller than 74% of U.S. dams with a recorded height. 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 Alton Twin Lakes-south Lake Dam
The primary purpose of Alton Twin Lakes-south Lake Dam is recreation. The dam creates a reservoir used for recreational activities such as fishing, boating, and swimming. The dam is owned by Harold Kinnard (private). It impounds the Trib West Fork Wood River near Alton.
The dam stands 32 feet tall and stretches 300 feet across, and has a maximum storage capacity of 200 acre-feet. Completed in 1970, the structure is well into its service life at over 50 years old.
This dam has a significant hazard potential classification, meaning that a failure could cause significant economic damage — flooding roads, bridges, or property downstream — but is not expected to result in loss of life. The most recent inspection on record was 08/20/2025.
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Location
| State | Illinois |
| County | Madison |
| Nearest City | Alton |
| River/Stream | Trib West Fork Wood River |
| Coordinates | 38.94573, -90.12622 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 32 ft |
| Dam Height | 32 ft |
| Dam Length | 300 ft |
| Year Completed | 1970 (56 years old) |
Storage & Hydraulics
| NID Storage | 200 acre-ft |
| Max Storage | 200 acre-ft |
| Normal Storage | 130 acre-ft |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Recreation |
| Owner | Harold Kinnard |
| Owner Type | Private |
| Hazard Classification | Significant |
| Condition Assessment | Not assessed |
| Last Inspection | 08/20/2025 |
| Emergency Action Plan | No |
Identifiers
| NID ID | IL00426 |
| Federal ID | IL00426 |
| More Info | State Dam Safety Program |