Health officials warned swimmers, surfers and snorkelers in Hawaii to stay out of the waters near Honolulu after a leak of 1,400 tons of molasses killed hundreds of fish, potentially attracting sharks.

So many fish had died by Thursday that the Hawaii Department of Health tripled cleanup crews to three boats, which removed hundreds of fish and were expected to remove thousands more, the department said in a statement.

A brown plume of sweet, sticky liquid was spotted seeping into Honolulu Harbor and Keehi Lagoon on Monday after a ship hauling molasses to the U.S. West Coast pulled out to sea.

By Tuesday, a leak was discovered in a molasses pipeline used to load it onto ships operated by Matson Navigation Company, the international ocean transport company, the health department said. Matson Navigation Company is a subsidiary of Matson Inc

Roger Smith, a dive shop owner who went underwater on Wednesday to survey the damage, said it was unlike anything he’d seen in 37 years of diving, with brown-tinted water and a layer of molasses coating the sea floor.

“Everything that was underwater suffocated,” Smith said. “Everything climbed out of its hole and the whole bottom was covered with fish, crabs, lobsters, worms, sea fans - anything that was down there was dead.”

The health department said in a statement that while molasses was not directly harmful to people, it was “polluting the water, causing fish to die and could lead to an increase in predator species such as sharks, barracuda and eels.”

Matson acknowledged in a statement that the spill was caused by a faulty molasses-loading pipe which it said has been fixed. It said molasses is a sugar product “that will dissipate on its own.”

Matson said it regretted the incident and was working with authorities to take steps to ensure it does not happen again.

“We take our role as an environmental steward very seriously,” the statement said. “We have a long history in Honolulu Harbor and can assure all involved that this is a rare incident.”

The health department said that “an unusual growth in marine algae” and harmful bacteria was another environmental danger posed by the spill. Molasses is a byproduct of the refining of sugarcane.

The department posted signs on beaches warning people to stay out of the water and not to consume any dead fish found in the area. The brown plume was expected to remain visible for weeks while natural tides and currents slowly flush the area, the department said.