Enterococci does not cause illness but is present in human intestines, so levels of the bacteria are used as a measure of how much raw sewage is in water.

Swimming sites rated as “poor” mean the water there is “susceptible to faecal pollution” and not always suitable for swimming, particularly three days after rainfall. It’s generally unsafe to swim at “very poor” rated areas because of the levels of sewage, microbes and pathogens in the water.

The testing process takes 24 to 48 hours, so there is no real-time indicator of water quality, but Beachwatch uses rainfall data to forecast contamination levels.

As a wet spring continues, Western Sydney University water scientist Dr Ian Wright advises swimmers to keep a keen eye on the Beachwatch forecast.

“This is really important information, particularly for people that have a weakened immune system or are very young, old or sick,” Wright said.

Swimming in polluted water carries a small risk of contracting gastro, hepatitis A and infections on the skin and in the ears, eyes, blood and respiratory tract.

“Anyone that swims in an estuary or coastal beach near an urban area should know ... you just don’t swim for a few days, because it’s very likely that you’re swimming through diluted sewage.”

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While more than three quarters of swimming sites and lakes and lagoons were susceptible to pollution, 94 per cent of NSW’s ocean beaches scored “good” or “very good” ratings.

Coogee Beach was the only beach in Sydney deemed poor.

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