Marsh Creek State Park was developed to help manage the water resources in the Brandywine Creek Watershed. Frequent flooding, water shortages, and lack of recreational opportunities were problems in the watershed.
The park was formerly a combination of rolling, wooded hills and small farms located on both sides of the Marsh Creek valley. The former village of Milford Mills is now under 30 to 50 feet of water. All of the buildings were removed; leaving only a few roads, foundations, and the embankments to the Larkin’s Bridge under the lake.
The lake was created by the damming of Marsh Creek. Construction of the dam occurred between May 1970 and June 1973. The impoundment is a 90-foot-high, 990-foot-long earth and rock fill dam on Marsh Creek, a tributary of the East Branch of Brandywine Creek.
On November 16, 1973, the gates of the dam were closed. The lake reached normal pool stage 218 days later on June 21, 1974.
At normal pool elevation of 359.5 feet above sea level, the impoundment covers an area of 535 acres plus a 25-acre wetland. The lake volume is 13,000 acre-feet (4.4 billion gallons) with a maximum depth of 80 feet at the dam.
The Marsh Creek watershed comprises 20 square miles of the Brandywine Creek watershed, which is part of the Delaware River Basin. The main tributaries in the watershed are:
- Marsh Creek
- Black Horse Creek
- Indian Run
- Jerry Run