Nearly half of Shenzhen's coastal waters were found to be seriously contaminated last year, and nine sewage drainage lines were found to be discharging excessive pollutants, according to a maritime study.
A professor of marine chemistry says the problem could worsen this year, as some temporary efforts to improve water quality last year for the World University Games are no longer in effect.
The 2011 study, issued on Wednesday by Shenzhen's Urban Planning and Land Resources Commission, found a total of 565 square kilometres of seriously contaminated seawater. Of the remaining waters, 145 square kilometres were lightly or moderately polluted, and 435 square kilometres were clean.
The contaminated waters were concentrated in Deep Bay and at the mouth of the Pearl River. Inorganic nitrogen and phosphates were the major pollutants.
Though the report covered only waters off Shenzhen, Professor Xu Hong , who has taught marine chemistry at Shenzhen University, said that the contaminated water could make its way to other areas, including Hong Kong.
He blamed illicit discharging of pollutants, along with a lack of oversight, for the heavy pollution. 'The government has been addressing excessive discharge through campaigns rather than regular monitoring and checks,' he said.
Xu said rapidly increasing pollution caused the high contamination levels in waters of western Shenzhen.
In comparison, seawater quality in the city's east was found to be much better. In Dapeng and Daya bays, both in east Shenzhen, the contamination level was in the first and second categories of the national seawater standards, indicating relatively clean water. But the water in Deep Bay - also known as Shenzhen Bay - and the mouth of the Pearl River was in the fourth category, the worst.
Excessively polluting sewage drains were found responsible for seriously contaminated water near the Kuichong River in the east, and near a sewage-treatment plant in the western Shekou Industrial Zone.
Nitrogen and phosphorus discharged from domestic sewage lines near Deep Bay and the mouth of the Pearl River, coupled with excessive heavy metals from industrial waste in the city's western region, are adversely affecting the marine ecosystem, the study found. There has also been oil pollution from the city's busy ports.
The water quality was better last year than in 2010, according to the report, which pointed to the efforts made ahead of the World University Games the city hosted in August.
Most areas off Shenzhen where seafood and other marine products are farmed met safety standards, as they are mostly in the east.
The two major beaches in the city, at the Dameisha and Xiaomeisha seaside resorts, also recorded good water quality last year, with the waters of Dameisha good for swimming for about 82 per cent of the 190 monitored days from April to October, while in Xiaomeisha the waters were good more than 93 per cent of the time.
of Shenzen's 15 coastal resorts, all in the east, were found to have good-quality water appropriate for recreational usage