It could take years for a "clean and green" state to fix its sewage-laden waterways, leaving unsuspecting swimmers at risk of pathogens and toxins.
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.
An 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, 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."
TasWater sustainable infrastructure general manager Matt Derbyshire said reducing bypass events and improving environmental performance is a key priority, saying it had sought $1.7 billion for upgrades to the system.
"The Tasmanian Economic Regulator recognised the need for this investment, however said investment should occur over a longer period of time, approving $1.2 billion in capital works over next four years," he said.
During the 2024/25 period, 100 out of 110 sewage treatment plants were in breach of their environmental protection notices, with treated wastewater released into the system exceeding maximum recommended levels for things like E. coli, phosphorus, and nitrogen.
The water campaigner said the huge nutrient load in freshwater ecosystems were putting the health of people and the environment at risk and could lead to oxygen-draining blue-green algal blooms.
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 and the Greens have called on Health Minister Bridget Archer to make the investments needed to upgrade the state's sewage systems and implement real-time monitoring of sewage pollution events.
