SOUTH Africa's seas are swimming with sewage, Deputy Environmental Affairs Minister Rejoice Mabudafhasi revealed on Friday.

Scientists have blamed excessive levels of nutrients in raw sewage for creating so-called "dead zones" in the ocean, where there is too little oxygen in the water to sustain life.

"South Africans are known to discharge more than 300-million litres of sewage every day into the marine environment," she said, "much of which is untreated or partially treated, and thus posing a serious threat to marine habitats, species and the public."

Ms Mabudafhasi was speaking at an event in East London to mark World Oceans Day.

The figure was later confirmed by the minister's spokesman, Peter Mbelengwa.

Ms Mabudafhasi said in a speech prepared for delivery that the volume of this sewage pollution was "increasing significantly", and South Africa had to find a better way of managing the problem.

Referring to dead zones in the world's oceans, she said: "We do not want these areas to appear in (the oceans of) South Africa and therefore we must find better ways of managing our waste."

The minister said she had attended a United Nations intergovernmental conference earlier this year where discussions were held on the need to tackle the causes of poor coastal water quality.

"At that particular meeting, which was attended by 65 countries, it was unanimously agreed that we should step up our efforts to tackle the damaging effects of sewage, marine litter and nutrients on our oceans," she said.

South Africa has 3000km of coastline, with hundreds of beaches used for recreation.

"Our beaches are much sought after by both South Africans and international visitors and are a major economic driver in the country's ever-growing tourism industry," the minister said. "As a country therefore, we (have) much to lose if we do not ensure that our beach waters are protected from pollution, because ultimately that pollution will affect us and our economy."