Tasmania's water authority released more than 47 billion litres of wastewater into state waterways in 2024/25, with over 600 million litres of that being under-treated sewage.
A new interactive map launched by non-government campaigners Environment Tasmania on Wednesday allows people to "Map the Crap" and check to see which waterways have been exposed to sewage pollution before they enter.
The "significant amount" of waste from TasWater's sewage treatment plants highlighted a huge pollution crisis across the state, the group's freshwater campaigner Lucy Tremain said.
"Anybody who's entering these waterways - swimmers, fishers, kayakers, rowers, paddle boarders - anyone who enjoys Tasmania's precious waterways are at risk of contamination from these pathogens and toxins," she told AAP.
"This is definitely a major risk to health and the clean and green image of Tasmania."
The plants, which are designed with a feature called a bypass event, treat wastewater multiple times before releasing it into waterways.
During a bypass event, sewage will skip "secondary treatment", meaning under-treated sewage, which can contain pathogens, nutrients and other contaminants that pose a risk to human health, is released.
It often occurs during large rainfall events or power failures at the plant.
"This is really an emergency safety mechanism that shouldn't be being used as part of the regular operations of a sewage treatment plant, but it is being used in that way," Ms Tremain said.
"It's the sign and symptoms of an aging and collapsing sewage infrastructure."
During the 2024/25 period, nine in 10 sewage treatment plants - 100 out of 110 facilities - were in breach of their environmental protection notices.
"The treated waste going into these same waterways is exceeding the maximum recommended levels for things like E. coli, phosphorus, and nitrogen," Ms Tremain said.
"On top of that, they're dumping in this under-treated sewage as well."
The water campaigner said the huge nutrient load in freshwater ecosystems were putting the health of people and the environment at risk.
"They can cause the growth of blue-green algae, which can cause ... all the oxygen to be removed from the water and suffocate other life," she said.
The environment group found the Prospect Vale plant released 27.5 million litres of under-treated sewage which flowed into Cataract Gorge, the Cameron Bay plant's 36 million litres polluted waters around the MONA building, and the Ti Tree Bend plant released over 338 million litres directly into the Tamar River.
Environment Tasmania is petitioning Health Minister Bridget Archer for real-time monitoring of the sewage pollution events.
"We want people to have all the information so that they can make those decisions for themselves. This is about prior consent," Ms Tremain said.
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