Several beaches that were closed Thursday because of high bacteria counts have been deemed safe for swimming and will be open this weekend, the state Department of Conservation and Recreation said Friday.

“All but two of DCR’s Boston and Metro Boston beaches are clean and unflagged/unposted,” or opened, the department said in a prepared statement.

Wollaston Beach at Channing Street in Quincy and Shannon Beach in Winchester remain closed after tests revealed elevated levels of bacteria, most likely caused by rainwater runoff earlier in the week, the state said.

Referring to the beaches that have been opened, the DCR said, “These beaches were precautionarily posted Wednesday following more than half an inch of rain Tuesday night.

“Tests on DCR’s Boston area beaches are done on Thursdays with results coming in on Friday midday each week. These tests allow us today to unpost the beaches.”

Orchard Beach and Rhoda Street Beach, as well as three different Wollaston beaches, were closed as a precaution Thursday. By Friday, those beaches were also reopened.

Quincy’s Back Beach, off of Delano Avenue, was reopened with a count of 10 colony-forming units per 100 milliliters of water. On Wednesday, the count was the highest it has been in years, at 6,015 units per 100 ml.

According to data from the Bureau of Environmental Health, the beaches were opened after having bacteria tests come back below the 104 colony-forming units per 100 ml of water – the cutoff for safe swimming standards.

Beaches are tested on a regular basis during warm-weather months in order to ensure the water is safe for swimming, DCR said.

High levels of bacteria in the water are not uncommon after rain, especially within the first 24 hours.