Dynegy/havana Sta/east Ash Pond System is an earth dam located in Mason County, Illinois, built in 1999. It carries a High hazard potential classification.
Dam profile
NID height · 38 ft38 ft tall and 3,800 ft long, taller than 84% 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 Dynegy/havana Sta/east Ash Pond System
Dynegy/havana Sta/east Ash Pond System is a dam in Mason, Illinois. The dam is owned by Dynegy Midwest Generation, LLC (public utility). It impounds the Trib Illinois River near Havana.
The dam stands 38 feet tall and stretches 3,800 feet across, creates a reservoir covering 18 acres, has a maximum storage capacity of 622 acre-feet, and collects water from a drainage area of 0 square miles. Completed in 1999, the structure is 27 years 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. An emergency action plan is in place for this dam. The most recent inspection on record was 10/07/2025.
At 38 feet, this dam is taller than 84% of dams nationwide.
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 | Mason |
| Nearest City | Havana |
| River/Stream | Trib Illinois River |
| Coordinates | 40.28139, -90.07428 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 38 ft |
| Dam Height | 38 ft |
| Dam Length | 3,800 ft |
| Year Completed | 1999 (27 years old) |
Storage & Hydraulics
| NID Storage | 622 acre-ft |
| Max Storage | 622 acre-ft |
| Surface Area | 18 acres |
| Drainage Area | 0 sq mi |
| Max Discharge | 244 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Other |
| Owner | Dynegy Midwest Generation, LLC |
| Owner Type | Public Utility |
| Hazard Classification | High |
| Condition Assessment | Not assessed |
| Last Inspection | 10/07/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | IL50420 |
| Federal ID | IL50420 |
| More Info | State Dam Safety Program |