Long Branch State Park's public beach remains open after an Aug. 31 water sample produced an E. coli geometric mean of 6.7 colonies per 100 milliliters.
The Missouri Department of Natural Resources samples designated state park beaches weekly during the recreational season. The two results used for the calculation were 5.2 and 8.6 colonies per 100 milliliters.
State law requires the department to post signs saying swimming is not recommended when the weekly geometric mean exceeds 190 colonies per 100 milliliters.
The department said a sample is a snapshot of water quality at the location and time it was collected and may not represent conditions throughout the lake.
The beach is open from sunrise to sunset through Monday, Sept. 7, according to Missouri State Parks.