Paper manufacturer Murim P&P and fisheries company Sajo are some of the biggest ocean polluters, according to an environmental report released Tuesday.
The list also included Chong Kun Dang, a pharmaceutical company; Harim, a chicken processing company; Hansol Paper; TS Corporation, a food company; Kumho Petrochemical; Hyosung Group and SKC.
The Korean Federation for Environmental Movements and Asian Citizen's Center for Environment and Health (ACCEH) said in the report that Murim P&P dumped 62,742 tons of wastewater into the ocean in 2014, which accounts for about 13 percent of the total amount Korean companies disposed of. The firm is likely to remain as the top contaminator this year as well, said the report.
Sajo is also a major polluter, with four of its subsidiaries disposing of wastewater into the ocean.
Korea is the only OECD member country that still allows ocean dumping.
In the face of mounting criticism from environmental groups and international organizations, the government has decided to ban these practices from next year.
Under the plan, all companies should first process the wastewater themselves.
"Although not even one year is left until dumping becomes illegal, companies haven't changed the way they do business," an ACCEH member said. "I hope this report will bring more attention to the reality."
Murim P&P and Sajo were among 407 companies that dumped industrial wastewater totaling almost 490,000 tons last year. This is equivalent to 50 million people throwing 10 kilograms of waste each into the sea.
For 2015, 319 companies submitted plans to the Ministry of Oceans and Fisheries to dump a total of 250,000 tons.
In Korea, ocean dumping began in the late 1960s and continued without any monitoring until the late 1980s.
In 1988, the government began to record the amount, which has grown continuously since then.
It reached 10 million tons in 2005, prompting then President Roh Moo-hyun to launch a campaign to reduce the pollution.
In 2012, the government announced it would prohibit the dumping from 2014, but this was changed under the Park Geun-hye administration, which gave a two-year grace period to companies for the transition.
Industrial wastewater is one of many forms of waste that is dumped into the ocean. The list includes food waste, chemical waste and livestock waste; however, industrial wastewater and sludge are the only kinds currently allowed by law to be disposed in the sea.
The law requires waste to be shipped off from six ports: Incheon, Busan, Ulsan, Gunsan, Pohang and Yeosu. Ulsan is the busiest port for wastewater, accounting for almost 40 percent of the country's total, followed by Gunsan, Incheon and Busan.
Three dumping sites were designated by law in the waters off Pohang and Ulsan in the East Sea and Gunsan in the West Sea. The site near Ulsan has been closed since 2013. The East Sea received 280,000 tons last year, 57 percent, while the rest was dumped in the West Sea.