The water quality at the upper beach at Hopkinton State Park returned to an unsafe level for swimming due to an increase in enterococci bacteria over the past week, according to water sample test results released Friday, while the water quality at the main beach remains unsuitable for swimming.

Last week, the bacteria level at the upper beach had returned to a safe level. Based on the testing of water samples this Thursday, a warning was announced Friday by the state’s Department of Conservation and Recreation. Ingesting or becoming submerged in bacteria-laden water can lead to symptoms including diarrhea and stomach pains.

Beaches statewide have been experiencing high levels of bacteria in recent weeks during the time of year when they are in the greatest demand for recreation. One cause is the amount of goose droppings in the water.

Lake Maspenock remains safe for swimming.