Seawater pollution remains serious in the coastal waters off south China's Guangdong province, where the marine ecological environment continues to deteriorate, officials said on Wednesday.

The seawater quality of the prosperous province has worsened since the monitoring began in 2001, according to the annual monitoring report released by the Guangdong provincial oceanic and fisheries administration on Wednesday.

The pollutant concentration of 45.3 percent of the total 95 monitored sewage outlets failed to meet the provincial requirements for pollutant discharge, the report showed.

"The Pearl River estuary, in particular, is the most polluted sea area of our province, with millions of tons of pollutants running into the South China Sea along with the river every year," Qu Jiashu, deputy director of the administration, said at a press briefing on Wednesday.

Based on data from observation stations in the shore areas of 14 coastal cities, the report showed that the seawater quality of Guangzhou, Dongguan and Zhongshan, as well as Shenzhen and Zhuhai, which neighbors Hong Kong and Macao, have fallen into the category of "seriously polluted".

Guangdong has a coastline of 4,114 km, the second longest among China's coastal provinces following the island province Hainan.

The report also showed the province saw 11 red tide incidents in the offshore area in 2009, as eutrophication has become a serious problem. The incidents affected 750 square km of sea, an area that has tripled since the level in 2008.

Red tide is a harmful algal bloom of phytoplankton that kills fish and reduces seawater quality. Such blooms often take on a red or brown hue, hence the name.

Inorganic nitrogen, phosphates and petroleum are the principal pollutants in the area, mainly due to discharge from heavy chemical industrial enterprises, said Wang Huajie, director of the provincial oceanic and fisheries environment monitoring center.

"The seawater pollution directly affects the life of local residents and also marine animals," he said.

Incidents like dolphins dying from eating discarded plastic bags that they mistake for food are frequently reported in the province, with the number of fish species continuing to decrease, he said.