Waste water has bypassed treatment plants and flowed into Sydney beaches eight times in as many weeks, the NSW opposition says, raising questions about the effectiveness of recent upgrades.

Swimmers at pollution hotspots north and south of Sydney have been urged to keep out of the water after recent heavy rainfall.

Opposition water spokesman Walt Secord says hundreds of thousands of litres of untreated water, including sewage overflows, have been allowed to flow into Sydney and Illawarra beaches.

'I acknowledge that we had rains, but these plants were supposed to have been upgraded to respond to such incidents,' he said.

The opposition says eight treatment plants were placed on bypass between February and April, meaning waste water went straight into waterways.

'These waste water treatment plants are coastal ones rather than deep ocean outfalls,' Mr Secord said.

But Sydney Water general manager of service delivery Eric de Rooy says claims that raw sewage was released into beaches are completely untrue.

'These waste water flows received screening, primary treatment and disinfection before being released,' he said in a statement.

'The waste water treatment plant is working as it is designed to do, and operating within the regulations set by the EPA.'

Sydney Water said on Thursday that a partial bypass had been put in place at Warriewood and Cronulla waste water treatment plants following heavy downpours across the city on Wednesday night.

Link:

Waste water polluting beaches - NSW oppn