A suspected oil tanker leak off the coast of Israel last week has led to Israel's biggest maritime ecological disaster in many years, with authorities closing the country's beaches and beginning a massive cleanup effort.

Chunks of sticky, black tar began washing up late last week. On Sunday, Israel's Environmental Protection Ministry warned people to avoid going to beaches from the country's northern border with Lebanon all the way to the south near the Gaza Strip. Tar exposure can make people sick and irritate the skin.

More than 4,000 volunteers from the Israeli nonprofit group EcoOcean have helped remove tar from beaches so far, according to the ministry.

The Israel Nature and Parks Authority warned that the "consequences will be seen for years to come."

Israeli environmental minister Gila Gamliel said Saturday that there are no more oil slicks visible off Israel's coast, "which is an encouraging condition." However the ministry warned that large waves are forecast this week. The waves could carry chunks of sticky tar from beach to beach, complicating cleanup efforts.

Israeli and European authorities are investigating what happened. Israeli officials believe a ship spilled tens or even hundreds of tons of oil in the Mediterranean, beyond the country's territorial waters.

The spill likely happened about a week ago, when stormy weather affected the region. It's unclear which ship or ships are responsible. Israeli authorities are working with European officials to review satellite images of ships that passed through the area.

The European Union monitors the location of oil slicks in the Mediterranean using information from a network of weather satellites. When ships release oil into the water, much of the oil pools at the surface and is carried great distances by currents. Scientists can use ocean current and weather data to reverse engineer the source of the tar that washed up along Israel's coastline.

Gamliel said Saturday that the ministry had zeroed in on fewer than a dozen ships, and was attempting to narrow it down further in the coming days, according to the Israeli newspaper Haaretz.

The tar pollution has already affected wildlife. Volunteers rushed to rescue sea birds, turtles and fish that were covered in oily residue or had ingested oil. Israel's National Sea Turtle Rescue Center confirmed that it was treating multiple turtles covered in tar.

One species that has ecologists particularly worried is a reef-building snail called Dendropoma petraeum.As the Mediterranean Sea heats up due to global warming, the snail's population on the Israeli coast has plummeted. That makes the species particularly vulnerable to other ecological disasters.

Daniel Estrin contributed reporting from Jerusalem.

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