An outbreak of E. coli O157 sickened at least 15 people who swam in the lake in mid- to late-July.
Among them was 2-year-old Madisyn Myers, whose mother said she received a clean bill of health Monday after three weeks of illness. The child had diarrhea and a urinary tract infection.
"It's hard to see your child go through that," said Michelle Myers of Hagerstown.
Representatives of three Pennsylvania agencies said Tuesday they know nothing new about the bacteria's source.
Specialized testing using federal Centers for Disease Control equipment has ended, and routine testing of lake and drinking water has resumed, according to Terry Brady, spokesman for the Pennsylvania Department of Conservation and Natural Resources.
The state closed Cowans Gap State Park's lake to all activities on Aug. 9. It reopened the Fulton County, Pa., lake to boating and fishing last week, but swimming continues to be prohibited.
Michelle Myers said she's leery of visiting the lake in the future.
"It was horrible," she said of her daughter's illness.
Madisyn Myers visited the park with her father and about 20 other people in the last weekend of July, according to her mother. The child was the only person from that group who was sickened.
Madisyn underwent stool and urine samples, catheterization and a day in the hospital. She lost four pounds, but the bacteria did not damage her kidneys as her mother feared.
"Monday was like a celebration for us," Michelle Myers said of receiving good test results.
Because the 42-acre lake is usually "swim at your own risk," it does not have a set season or official closing date on a usual year, Brady said.
Testing on Aug. 15 showed E. coli bacteria in untreated water from one of the park's two wells. Officials said that bacteria was not from the E. coli O157 strain, but they shut down the well temporarily, chlorinated the water and issued a boil-water advisory that has since been lifted.