Israel’s Ministry of Health warned the public not to enter several streams in the Golan Heights after nearly 30 people were hospitalized with bacterial infections after spending time in the water.

The Israel Nature and Parks Authority announced that the Yehudiya, Zaki, Zavitan and Meshishim streams are not currently safe for entry, after 27 people contracted Leptospirosis after swimming in the bodies of water since July 1—20 of them arriving in the last few days.

Hundreds of people who visited the popular swimming spots will be examined and possibly treated in hospitals, according to the ministry.

Other streams in northern Israel, which are attractions for the thousands of Israelis and tourists who travel the country during the hot summer months, have been approved by health officials for swimming purposes.

Symptoms of the illness, which frequently mimic the flu, can often be mild. But more serious infections can lead to liver and kidney problems, and even meningitis.