Lake Mendota Dam is an earth dam located in LaSalle County, Illinois, built in 1890. It carries a High hazard potential classification.
Dam profile
NID height · 17 ft17 ft tall and 2,430 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 Lake Mendota Dam
The primary purpose of Lake Mendota Dam is recreation. The dam creates a reservoir used for recreational activities such as fishing, boating, and swimming. The dam is owned by City of Mendota (local government). It impounds the Mendota Creek near Mendota.
The dam stands 17 feet tall and stretches 2,430 feet across, creates a reservoir covering 17 acres, has a maximum storage capacity of 246 acre-feet, and collects water from a drainage area of 221 square miles. Completed in 1890, the structure is over a century old.
This dam carries a high hazard potential classification, which means that a failure or uncontrolled release of water would likely cause loss of human life. This classification reflects the consequences of failure, not the likelihood — it indicates that people live or work in the area downstream. Notably, no emergency action plan is currently on file for this high-hazard dam. The most recent inspection on record was 04/29/2025.
Living Downstream
If you live or work downstream of this dam, consider taking these steps: learn your local evacuation routes, check whether your county emergency management office has a dam failure inundation map, and sign up for local emergency alerts. The Illinois dam safety program can provide more specific information about emergency planning for this structure.
Search for dams near your address to see all dams in your area with hazard classifications and safety data.
Location
| State | Illinois |
| County | LaSalle |
| Nearest City | Mendota |
| River/Stream | Mendota Creek |
| Coordinates | 41.55705, -89.12874 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 17 ft |
| Dam Height | 17 ft |
| Dam Length | 2,430 ft |
| Year Completed | 1890 (136 years old) |
Storage & Hydraulics
| NID Storage | 246 acre-ft |
| Max Storage | 246 acre-ft |
| Normal Storage | 163 acre-ft |
| Surface Area | 17 acres |
| Drainage Area | 221 sq mi |
| Max Discharge | 860 cfs |
| Spillway Type | Controlled |
Ownership & Safety
| Purpose | Recreation |
| Owner | City of Mendota |
| Owner Type | Local Government |
| Hazard Classification | High |
| Condition Assessment | Not assessed |
| Last Inspection | 04/29/2025 |
| Emergency Action Plan | No |
Identifiers
| NID ID | IL00223 |
| Federal ID | IL00223 |
| More Info | State Dam Safety Program |