Significant levels of strong pain killers and anti-depressants have been found in tests done on water samples in Sydney Harbour, University of Sydney scientists say.
The drugs are believed to be coming from sewage pipes leaking into storm water pipes.
The drugs were found by analysing samples of marine water from 30 sites adjacent to stormwater outlets across the entire Sydney estuary.
Scientist Greg Birch from the School of Geosciences at the University of Sydney said it was the first time this kind of research had been done in Australia.
"I was surprised how widespread the drugs were in the samples. paracetamol was found in all 30 sites, whereas one particular artificial sweetener was found in 27 sites," he said.
Other drugs found across Sydney Harbour waters included beta blockers and an epilepsy medication.
Mr Birch said the findings indicated sewage water may be leaking into the harbour.
"The presence of acesulfame [a recognised marker of domestic wastewater] and pharmaceuticals in water from all parts of the estuary after a dry period, suggests sewage water is leaking into the stormwater system in this catchment," he said.
While the drugs were widespread in Sydney Harbour waters, they were found in low concentrations. It is not known whether the leak is harmful to humans, flora or fauna.
"When this has happened in other areas, it certainly has had an impact on the fish and environment," Mr Birch said.
Researchers said sewage water was not discharged to the estuary, except infrequently when it overflowed during periods of high rainfall.
According to the findings, which were detailed in the latest issue of Marine Pollution Bulletin, drugs were detected in all parts of the Sydney estuary, but were higher in Duck River and to a lesser extent Parramatta River, lower Lane Cove and Rozelle Bay.
Seven different pesticides were also detected.
"The pesticides are applied to the environment and were discharged via stormwater to the estuary," the researchers said.
Researchers said this was the first study to report micro-pollutants in the Sydney estuary and some pesticides in Australian marine waters.
They also looked for nine antibiotics and personal care products but none were identified.