Health officials yesterday 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 yesterday 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 Harbour and Keehi Lagoon on Monday after a ship hauling molasses to the US 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

“While molasses is not harmful to the public directly, the substance is polluting the water, causing fish to die and could lead to an increase in predator species such as sharks, barracuda and eels,” the health department said in a statement.

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.”

But the company expressed regret over the incident and said it was working with authorities and would 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 Harbour and can assure all involved that this is a rare incident in our longstanding Sand Island operation.”

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.