St. Marys Lake Dam
Key Takeaway
St. Marys Lake Dam is classified as high hazard in Illinois. It was completed in 1921 and is 105 years old. Its primary use is recreation. High hazard means loss of life is likely if the dam fails — it does not indicate the dam's current condition. Learn more.
Physical Details
| Dam Height | 12 ft (taller than 10% in IL) |
| Dam Length | 389 ft |
| Dam Type | Gravity |
| Max Storage | 966 acre-ft |
| Normal Storage | 778 acre-ft |
| Surface Area | 96 acres |
| Drainage Area | 3 sq mi |
| Max Discharge | 320 cfs |
| Year Completed | 1921 (105 years old) |
| NID ID | IL00654 |
Safety Information
Loss of human life is likely if the dam fails.
Hazard potential describes downstream consequences of failure, not the dam's current condition. What does this mean?
Ownership
ARCHDIOCESE OF CHICAGO
Private
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High Hazard 11 ftFrequently Asked Questions
What is the hazard classification of St. Marys Lake Dam?
St. Marys Lake Dam is classified as High Hazard. Loss of human life is likely if the dam fails. This classification refers to the potential downstream consequences of a failure, not the dam's current structural condition.
Who owns and operates St. Marys Lake Dam?
St. Marys Lake Dam is owned by ARCHDIOCESE OF CHICAGO (Private). The owner is responsible for maintenance, inspections, and compliance with dam safety regulations.
When was St. Marys Lake Dam built?
St. Marys Lake Dam was completed in 1921, making it 105 years old. Many U.S. dams were built between the 1930s and 1970s during a period of major infrastructure investment.
What is the primary purpose of St. Marys Lake Dam?
St. Marys Lake Dam serves the following purposes: Recreation. Many dams in the U.S. are multi-purpose, supporting flood control, water supply, recreation, and other uses.
How tall is St. Marys Lake Dam?
St. Marys Lake Dam has a dam height of 12 ft. Dam height is measured from the natural streambed at the downstream toe to the top of the dam, and may differ from the visible height.
When was St. Marys Lake Dam last inspected?
St. Marys Lake Dam was last inspected on December 31, 2020. Inspection dates indicate when a formal review occurred, not the results of that inspection.