Three Lake Kinneret beaches were shut down by the Health Ministry on Thursday to protect bathers from pollution: the beach at Tiberias, and the Ganei Hemat and Sironit beaches south of the city. Lake Kinneret was found to be contaminated for the third time in recent weeks, ministry officials said. Fecal coliform was present off the beaches at twice the permitted levels, most likely from a sewage leak, they said. "When you close a beach, it's because pollution occurred five days earlier," said Dr. Aaron Dotan, head of Water Sciences at the Israel Union for Environmental Defense (Adam Teva V'din). This time lapse could mean that the water is clean by the time a beach is closed to swimmers, Dotan said, and it also means there are swimmers in the lake while the pollutants are present. Dotan said testing the water after the fact was therefore useless in protecting the public's health. "You have to treat the sources of pollution, because just closing the beach is not effective," he said. On Sunday, the Health Ministry closed two beaches near Tiberias, after the municipality allowed sewage to run into the lake for approximately one hour. These increasingly common leaks pose a major threat to the Sea of Galilee's tourist industry, which attracts Jews and Christians alike. The Kinneret Basin is the largest single source of Israel's drinkable water, constituting 33 percent of the national water bank.