More than 100 miles (161 kilometers) of Israel’s normally pristine Meditteranean coastline have been stained with thick globules of tar that washed up after an oil spill off the coast of the country last week. Authorities have yet to identify the culprit, but they say it is harmful to both humans and marine life.

Israel’s Nature and Parks Authority (INPA) called the spill “one of the most serious ecological disasters” the country has ever seen and warned it could take years to completely remove the waste from beaches, according to the BBC.