A massive molasses spill in Honolulu Harbor will require a lot of clean-up, and will have a long-term impact on fish and other marine wildlife, authorities say.

"It's in a bay, so there's not a lot of circulation, so you're not going to have flushing of this water out," biologist David Field said. "So, in this area where the spill occurred, we're going to see the effects probably for a long time."

The molasses spill dumped as much as 1,400 tons, or 233,000 gallons, of molasses into the harbor. The case might be the biggest they've had to confront in Hawaii, the Hawaii Department of Health said.

"This is the worst environmental damage to sea life that I have come across, and it's fair to say that this is a biggie if not the biggest that we've had to confront in the state of Hawaii," Deputy Department of Health Director Gary Gill told Hawaii News Now.

Thousands of dead fish litter the ocean floor in Honolulu Harbor, underwater video reveals. Authorities are scooping colorful dead fish bobbing on the top with nets.

"It seemed like they were trying to gasp for air," Sachi Uehara, a resident, said. "There were, I would say, over 50 eels that were up at the surface that we could see."

Field, who is an assistant professor of marine sciences at Hawaii Pacific University, said that the molasses spill may spread. "As water does leave this bay area and goes out into the neighboring ocean, we can expect the effects in the long term, in days, weeks, months and probably years, to spread out over some of the soft-shore reefs," he said.

Authorities are also worried about an increase in predators and growth in marine algae due to the nutrient-rich molasses. They warned against eating fish, saying,

"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.