Thousands of residents helped with the clean-up, saying there was nothing else to do now that tourism has died in a region famed for its sandy beaches. Fisheries ground to a halt.
Kim Soo-ha, 63, wept at her oyster farm as she held dead shellfish coated in tar.
"I sent my kids to college by making money from this," she said. "I don't know how I'm going to live. They say they can't do anything about it for the next 10 years."
Environmental groups say oil in the Taean seabed and the loss of food for aquatic species will cause damage to the ecosystem that will last for years.
Hotels in the region are vacant and several restaurants that catered to tourists posted signs in their windows reading: "The government needs to pay".
South Korea has declared the region a disaster area but initially freed up only a little over $6 million in aid. It has yet to give an estimate for the damage.
A maritime ministry official said the country lacked enough clean-up equipment and was ill prepared, Yonhap news agency said.