A massive algal bloom off the coast of Kep that has left scores of dead coastal crabs and fish in its wake resulted in warnings from the Ministry of Environment and Prime Minister Hun Sen this weekend to avoid eating seafood or swimming in the seaside province.

“The Ministry of Environment appeals to the public, especially tourists and people living along the sea in Kep province, to temporarily stop swimming in the sea or eating seafood caught there,” reads the statement issued by the Ministry of Environment on Saturday.

Its words of warning, which come little more than a week before the expected throngs of tourists for Khmer New Year, were echoed by the prime minister in a Facebook post that evening.

An algal bloom is a sudden overgrowth of algae brought on by a variety of ecological factors, including warming water temperatures, an excess of waterborne nutrients and various hydrological conditions such as shifting currents.

They occur throughout the world in both marine and freshwater environments. When blooms die, the algae collect in long, slimy stripes that float on the surface and wash ashore in unsightly, putrid piles.

When decaying, the dead algae sucks oxygen from the water and can suffocate sea life. In certain conditions, blooms can “produce potent toxins that contaminate seafood and can even kill humans”, according to Gustaaf Hallegraeff, an expert on harmful algal blooms at the University of Tasmania.

Ministry of Environment officials are currently monitoring water samples from Kep for toxicity levels, according to Kuch Virak, director of Kep’s Fisheries Administration cantonment, but have yet to reach any conclusions, he said yesterday.

According to a leading conservationist in Kep who is working with authorities, the recent bloom, normally a natural, yearly phenomenon, was likely exacerbated in this case by manmade factors.

“I believe the largest contributing factor is the illegal bottom-trawlers working in the areas between the islands and the mainland,” said Paul Ferber, director of Marine Conservation Cambodia, in a phone interview yesterday. Illegal bottom-trawling has in recent years become an epidemic in Kep Bay, according to officials there.

Ferber theorised that decomposing sea grass ripped from the seafloor by the trawlers’ nets had created an unnaturally nutrient-rich environment for plankton, which is the main food source for Noctiluca scintillans, the microorganism that makes up algal blooms. Higher levels of plankton would have fed and intensified the bloom, he reasoned.

“This event happens more than once a year in Kep. [The plankton] acts as a natural food source that is usually beneficial to the ecosystem, but as the ecosystem is close to collapse, this one had a very negative impact,” he said.

Cheam “Chris” Oeun, who manages the Democrat, a seafood restaurant near Kep’s popular crab market, said that despite the government warning, he was still serving local seafood. Oeun said he believed the warning not only to be an overreaction on the government’s part, but also a potential threat to his livelihood.

“I am concerned that the Ministry of Environment is telling people not to eat seafood here,” he said. “Khmer New Year is coming up. If people don’t come here for seafood, our business will have many problems. We won’t have any money.”

Kien Wagnir, the German head chef for the upscale Sailing Club and Strand restaurants in Kep, was treating the situation more cautiously.

“Until we have 100 per cent certainty on what’s going on with the water, we are not serving seafood from Kep,” he said, before adding, “This is really not good for the reputation of Kep.”

Wagnir added that rumours were spreading in Kep that the bloom was somehow caused by a chemical agent leaked by Vietnamese factories. The unsubstantiated claim was alluded to dismissively by Ministry of Environment spokesman Sao Sopheap yesterday.

“According to our examination, the rumour claiming that a chemical substance caused the bloom is not reputable. This is just a natural phenomenon because our country is affected by rising temperatures,” he said, referring to scientific theories linking the frequency and intensity of algal blooms to climate change.

According to officials and Kep residents, the bloom had shown signs of subsiding yesterday but had not yet fully cleared.