Regional authorities yesterday threatened to close down the main Athens waste treatment plant unless action is taken, before the Olympics, to remove the hills of malodorous sludge that have piled up on the offshore site due to problems at the capital’s landfill. In a letter to Public Works Minister Giorgos Souflias, Piraeus prefect Yiannis Michos said some 80,000 tons of muck have accrued over the past 15 months on the islet of Psyttaleia, between the country’s largest port and the island of Salamina, posing a major public health risk. Michos said prefectural officials estimate the sludge will reach 150,000 tons by August, when the Olympics are to be held, unless action is taken. The solid residue of the waste treatment system was initially sent to the congested Ano Liosia rubbish dump, but shipments were stopped after the sludge caused landslides last March. In April, Souflias told Parliament that Psyttaleia could only store sludge for another three to five months.