Israel closed all its Mediterranean beaches until further notice Sunday, days after an offshore oil spill deposited tons of tar across more than 160 kilometers (100 miles) of coastline in what officials are calling one of the country’s worst ecological disasters.

Activists began reporting globs of black tar on Israel’s coast last week after a heavy storm. The deposits have wreaked havoc on local wildlife.

Israel’s Nature and Parks Authority has called the spill “one of the most serious ecological disasters” in the country’s history. In 2014, a crude oil spill in the Arava Desert caused extensive damage to one of the country’s delicate ecosystems.

The Environmental Protection Ministry and activists estimate that at least 1,000 tons of tar, a product of an oil spill from a ship in the eastern Mediterranean earlier this month, have washed up on shore. The ministry is trying to determine who is responsible.

The Environmental Protection, Health and Interior Ministries issued a joint statement Sunday warning the public not to visit the entire length of the country’s 195-kilometer (120-mile) Mediterranean coastline, cautioning that “exposure to tar can be harmful to public health.”