Moraine State Park is a Pennsylvania state park on 16,725 acres in Brady, Clay, Franklin, Muddy Creek, and Worth townships in Butler County, Pennsylvania. The park includes a man-made lake, Lake Arthur, formed by impounding Muddy Creek, which is 3,225 acres and is used for recreational purposes. The surrounding park is used for hiking, bicycling, group camping, picnicking, and hunting. Moraine State Park hosts the annual Regatta at Lake Arthur in August.