China's oceanic authorities said on Wednesday the country's coastal waters were seriously contaminated in 2014, following a national political adviser's call for marine environment protection on Tuesday.

Of the areas monitored by the State Oceanic Administration (SOA) in the summer of 2014, 81 percent, or 41,000 square kilometers, was polluted. It said most of the polluted areas were concentrated in river estuaries or sea bays, such as the Yangtze River and Pearl River estuaries as well as the Bohai Gulf, according to a 2014 national report on marine environment quality issued by the SOA.

The situation had only slightly improved from the previous year, when the SOA recorded 44,340 square kilometers of polluted sea waters in the 2013 report.

Zhang Meizhi, a Central Committee member of the China Association for Promoting Democracy, one of the eight democratic parties, has proposed the introduction of unified rules on government supervision over marine contamination and to restructure the layout of industrial plants along the coast of the Bohai Gulf, when she discovered heavy pollution in the area.

Some 2.8 billion tons of sewage and 700,000 tons of contaminants were dumped into the Bohai Gulf annually, accounting for half of the nationwide pollutants, Zhang said in the ongoing two sessions.

The SOA pointed out that inorganic nitrogen, reactive phosphate and oil are the three major pollutants.

Oil is mainly discharged from boats in rivers, while nitrogen and phosphate pollution come from sanitary sewage and the widespread use of chemical fertilizers, Dai Xingyi, director of the Urban Environmental Management Research Center at Fudan University, told the Global Times.

"The government, which has long failed to keep an eye on discharges from boats, should require vessel operators to install sewage treatment facilities," Dai said.

Ma Jun, director of the Institute of Public and Environmental Affairs, also urged the government to tighten supervision over sewage treatment plants that discharge substandard sewage to rivers and the ocean.

Dai added that "even if the sewage reaches the national standard, many cities clustered along the coast that accumulate waste could still contaminate the sea."

Marine disasters such as red tides and green algae also had a larger impact on the sea in 2014 than in 2013, according to the report.