Ranked: The cleanest and dirtiest beaches in Sydney

The NSW government’s BeachWatch program takes regular samples at swim sites around NSW, including nearly 100 beaches and river baths in Sydney, and it measures the colony forming units (cfu) of Enterococci bacteria per 100 millimetres of water.

Enterococci live in the guts of warm-blooded animals and can cause severe gastrointestinal illness. The bacteria are an indicator of faecal matter in water and often occur alongside another serious pathogen, E. coli.

Swimming is considered safe when the number of colony-forming units of Enterococci bacteria is less than 41 per 100 millilitres of water.

The Herald analysis used all the data from October 15, 2024 to October 14, 2025, and ranked sites by the median or midpoint number. Statistically, this is closer to the typical result than the average or mean, which can be skewed by outlier results.

Avalon Beach had a median level of 0cfu per 100ml, its average result was 1.4cfu per 100ml and its worst result was 28cfu per 100ml on December 13, 2024, still well under the safe threshold.

This was music to the ears of Lachlan Carlton, 16, who swims at Avalon almost every day after school.

“It’s good to hear your beach is clean,” Carlton said. “I think all the locals in the area love the ocean and are very aware of keeping it clean and respecting the environment. Maybe that’s a contributing factor to why it’s so clean.”

Bayview Baths had a median result of 35cfu per 100ml and 49 per cent of the readings were above 40. The worst day was November 15, 2024, when it reached 2600cfu per 100ml.

Wright said a median of 35 was bad because it meant that half the time it would be above 35. He was nervous when the median hit the 20s, though if the water looked and smelled OK, he would probably still swim, perhaps keeping his head above water.

“It is bacterial roulette,” he said. “You actually never know how much bacteria is in the water, or other pathogenic organisms, such as viruses and parasites.”

A statement from Northern Beaches Council said the BeachWatch program captured both wet and dry conditions, and it was an official recommendation not to swim for at least one day after heavy rain at ocean beaches, and up to three days at estuarine swimming areas such as Pittwater, because of stormwater runoff.

Bayview Baths is scheduled for an upgrade costing nearly $800,000 including a new wharf, new ramp/gangway, a wharf extension to provide more dinghy boat tie-ups, a kayak entry and exit point, a new wider tidal pool allowing for up to 25-metre lap swimming, and accessibility improvements. Work will start in the middle of next year.

Bayview and Church Point Residents Association president Peter Blanchard said surveys showed the community was strongly supportive of restoring and upgrading the baths.

“They’ve deteriorated to the point where they’re actually no longer a functional set of baths, and in fact, they haven’t been for several years, and our association has been lobbied for … probably 12 years to try and get them repaired,” Blanchard said.

“There were concerns about pollution because of stormwater drainage near the area … but we’ve been reassured it’s now safe.”

While there might be individual episodes where the water was too dirty to swim, Blanchard said he expected that would be monitored and communicated to residents, as it was at other sites.

Of the eastern beaches, Bondi and Little Bay had the worst median results, but at 11cfu per 100ml, they were relatively clean. South Maroubra, with a median of 2cfu per 100ml, was the cleanest of the eastern beaches. In the Sutherland Shire, North Cronulla was 10.5cfu per 100ml and South Cronulla was 5cfu per 100ml.

Sydney Harbour and Parramatta River were the cleanest of Sydney’s estuaries. All sites showed a low median pollution reading. Even up river, Cabarita registered 2.5cfu per 100ml and Chiswick just 4cfu per 100ml.

Dawn Fraser Baths in Balmain, which recorded alarmingly high readings when the Herald commissioned its own testing last summer, had a median of 3cfu per 100ml.

University of Sydney civil engineering and water quality expert professor Stuart Khan said the waterways were much cleaner than 30 to 50 years ago.

The construction of the deep-water ocean outfalls off North Head, Bondi and Malabar in the early 1990s improved water quality at ocean beaches significantly, he said, and Sydney Harbour and Parramatta River no longer had industrial discharge. The heavy industry on Parramatta River once included chemical manufacturing and ship building, and before that, abattoirs, tanneries and whaling stations.

“The same general trends also apply to other waterways such as the Georges River and Botany Bay,” Khan said.

“However, Botany Bay also has some more contemporary sources of pollution, including Sydney Airport, heavy industry, and a major wet-weather sewage overflow point, which is likely getting worse as an increasing number of homes are connected to that sewer.

“There are some pollutants, such as PFAS, that we didn’t pay much attention to 30 years ago, but are now discovering to be widespread in urban waterways.”

Khan said stormwater runoff brought chemicals and debris from urban areas into the waterways, while heavy rainfall could also flood the sewerage pipes and make them overflow into the stormwater.

Annual assessments of water quality tend to show improvements during very dry years, and deterioration during very wet years, Khan said, but these effects were not lasting.

The NSW government will release its State of the Beaches report for 2025 soon. This will also draw on BeachWatch data, but it is likely to use different dates and methodology.

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