Unfortunately, the south end and middle of Blackmans Bay beach have been downgraded to poor as a result of the outcomes of the 2025/26 sampling program. This means that swimming is not advised in these two locations. It is generally safe to swim at the rest of the beach.
What does a “Poor” rating mean?
Blackmans Bay Beach
This doesn’t mean the water quality is poor every day. A sample is a snapshot in time, and it only tells us what the water quality is like at that specific place and time. The long-term rating is based on five years of sampling data from a Tuesday sample between December and March with only 5 significant failed samples needed during that period for the water quality rating of a beach to be downgraded.
UNDERSTANDING WATER QUALITY AT BLACKMANS BAY BEACH
Council understands the community expects answers about water quality at Blackmans Bay Beach.
Research has shown that water quality at Blackmans Bay is influenced by a range of interconnected factors rather than a single source of contamination. This means there is no single cause or simple fix.
A good beach water quality result does not necessarily mean nearby stormwater outfalls are free from contamination, and poor beach water quality results do not always indicate that contamination is coming directly from the outfalls.
For this reason, Council has looked beyond individual test results to develop a broader understanding of how the stormwater network, local environment and natural conditions within the bay interact to influence water quality.
INVESTIGATIONS
Independent investigations indicate that water quality at Blackmans Bay is influenced by a range of interconnected factors, with leaking sewer infrastructure entering the stormwater network identified as the most common likely contributor.
Leaks can occur through sewer overflows, infrastructure failures and the gradual deterioration of ageing assets. Working with TasWater, Council has identified and addressed many defects and potential contamination pathways throughout the catchment network. While this work has improved the system and expanded understanding of the issue, ageing infrastructure means new faults will emerge over time.
The challenge is compounded by the size and complexity of the stormwater network. Three of Blackmans Bay Beach’s four stormwater outfalls are located at the southern end of the beach, where water quality issues are most persistent.
Together, these outfalls collect runoff from more than 3,000 properties and approximately 20 kilometres of roads. Anything washed into the stormwater system travels through around 75 kilometres of underground pipes before reaching the bay, creating a large and complex network through which contamination can enter.
INDEPENDENT ANALYSIS
In 2025, Council engaged independent environmental consultants Marine Solutions to investigate the factors influencing water quality at the southern end of Blackmans Bay Beach.
The investigation included a review of previous studies, water quality monitoring data and testing results from both the beach and the stormwater network, as well as field investigations designed to better understand how stormwater moves through the bay.
As part of the investigation, Marine Solutions used a bright green dye called Fluorescein to trace how water discharged from stormwater outfalls moves through the bay. Fluorescein is a non-toxic, biodegradable dye that is widely used in environmental studies to track water movement. The dye was monitored over multiple tidal cycles to better understand how stormwater disperses once it enters the marine environment.
The investigation found that natural conditions within Blackmans Bay play an important role in influencing water quality outcomes. The shape of the bay means water does not flush through as quickly as it does at many other beaches in the Derwent, allowing contaminants to remain in the shallow waters along the southern shoreline for longer periods.
As a result, even relatively small contamination events can have a greater impact than they might in areas with stronger water movement and faster flushing. These environmental conditions, combined with the size and complexity of the surrounding catchment, contribute to the ongoing water quality challenges experienced at the southern end of the beach.
The investigation also confirmed that the issue is shaped by several interacting factors, including the large catchment that drains to the southern end of the beach, ageing infrastructure within the broader network, stormwater inputs from thousands of properties, and the natural characteristics of the bay itself. Together, these factors help explain why improving water quality at Blackmans Bay is a complex challenge and why there is no single source or simple solution.
Recreational Water Quality Investigation
Preliminary estimates suggest a project of this scale would cost several million and would likely require substantial State or Federal Government funding.
Constructed Wetlands
Another option is the construction of a treatment wetland to filter stormwater before it enters the bay. Wetlands can help remove sediments, nutrients and other pollutants while also providing broader environmental benefits.
However, a project of this scale would require a substantial area of suitable land, and there is currently no suitable location available in Blackmans Bay.
Ongoing Commitment
While there are no quick or simple solutions to a complex issue, Council remains committed to working with TasWater, the Derwent Estuary Program and other stakeholders to investigate practical improvements and pursue opportunities to improve water quality over time.
Ongoing monitoring, investigation and collaboration remain essential to understanding contamination sources and identifying effective responses.
HOW THE COMMUNITY CAN HELP
The community also has an important role to play in protecting water quality.
Many people are surprised to learn that stormwater drains flow directly to local waterways and beaches. Anything left on roads, driveways, footpaths or gutters can eventually be washed through the stormwater system and into Blackmans Bay.
Residents can help improve water quality by:
- Keeping litter, chemicals and other pollutants out of stormwater drains.
- Disposing of waste responsibly.
- Avoiding flushing unsuitable items down toilets and household drains.
- Picking up pet waste.
- Reporting suspected sewer spills or overflows to TasWater.
Small actions taken across the community can make a meaningful contribution to improving the health of local waterways and the long-term water quality of Blackmans Bay.
FAQ’s
Why has Blackmans Bay South and Middle Beach been downgraded?
The Derwent Estuary Program assesses beach water quality using a five-year record of monitoring results. A beach section is downgraded when a specified number of poor results are recorded over that period.
The downgrade does not mean the beach is always unsafe to swim at. It reflects the long-term performance of the site based on nationally recognised assessment criteria.
Does a "Poor" rating mean the water is always contaminated?
No.
A “Poor” rating does not mean water quality is poor every day. Blackmans Bay frequently records water quality results that meet recreational water quality guidelines. However, repeated poor results over a five-year period can trigger a downgrade under the assessment framework.
Is it safe to swim at Blackmans Bay Beach?
Swimming is currently not advised in the areas subject to the no-swim advisory.
Water quality can vary across the beach and over time.
Council recommends checking current advice and following any signs and public health warnings before entering the water.
What is causing the water quality issues?
Independent investigations indicate that water quality at Blackmans Bay is influenced by a number of interconnected factors rather than a single contamination source.
The evidence suggests the most common likely contributor is contamination entering the stormwater network, including from ageing sewer infrastructure, sewer spills, stormwater runoff and other sources spread across the catchment.
Why is it so difficult to find the source of contamination?
Blackmans Bay is serviced by a large and complex stormwater network.
Three stormwater outfalls at the southern end of the beach collect runoff from more than 3,000 properties and around 20 kilometres of roads. Water travels through approximately 75 kilometres of underground pipes before reaching the bay, creating many potential pathways for contamination to enter the system.
What exactly has been detected in the water?
Enterococci is the indicator used in the summer monitoring program.
Enterococci levels in these samples are measured in cfu/100ml (colony forming units per 100mls).
Enterococci is a faecal bacterium that is indicative of the presence of sewerage but can also be present from other natural sources in the environment such as agricultural runoff, birds and animals faeces.
Water contamination by sewage and animal faeces may pose a health hazard when the water is used for primary contact recreation, such as swimming.
What has Council done so far?
Council has undertaken extensive investigations into the issue over many years.
This work has included hundreds of water quality samples, source tracking through the stormwater network, contamination investigations, ammonia testing, infrastructure inspections and collaboration with TasWater and the Derwent Estuary Program. Council has also engaged independent environmental specialists to review the evidence and recommend further investigations.
What did the independent investigation find?
In 2025, Council engaged Marine Solutions to independently review the available evidence and investigate how stormwater may be affecting water quality.
The investigation found that several factors are likely contributing to the issue, including ageing infrastructure, the large stormwater catchment draining to the beach, and the way water moves within Blackmans Bay. The report concluded that the issue is complex and cannot be attributed to a single source.
How does the shape of Blackmans Bay affect water quality?
The shape of Blackmans Bay means water does not flush through as quickly as many other locations in the Derwent.
This can allow contaminants entering the bay to remain in shallow waters near the southern shoreline for longer periods, increasing the potential impact on recreational water quality.
Why don't stormwater test results always match beach water quality results?
The relationship between stormwater contamination and beach water quality is not always straightforward.
A clean beach sample does not necessarily mean nearby stormwater outfalls are free from contamination, and a contaminated outfall does not always result in a poor beach water quality result. Tides, currents, rainfall, water movement and the shape of the bay can all influence conditions at any given time.
Why can't Council simply fix the problem?
Council and TasWater continue to identify and address contamination sources as they are discovered.
However, the network is large, much of the infrastructure is ageing, and new faults can develop over time. Water quality is also influenced by environmental factors that cannot be easily controlled. This means improvement requires ongoing investigation, maintenance and collaboration rather than a single fix.
Why not extend the stormwater pipes further offshore?
Extending the stormwater outfalls further into the Derwent is one potential long-term option that could improve dispersal.
However, preliminary assessments indicate a project of this scale could cost many millions of dollars and would likely require substantial support from State or Federal governments.
Why not build a treatment wetland?
Constructed wetlands can help improve stormwater quality by filtering pollutants before water reaches waterways.
While this option offers environmental benefits, it requires a significant area of suitable land, and there is currently no suitable location available in Blackmans Bay for a wetland of the scale required.
What is Council doing next?
Council will continue working with TasWater, the Derwent Estuary Program and independent specialists to better understand contamination sources and investigate practical options to improve water quality over time.
Monitoring, sampling and investigation work will continue to guide future decision-making.
I went swimming in the ‘poor’ section, will I be, okay?
It is unlikely that you will become sick.
As always, if you are concerned, we would encourage you to talk to your GP or other healthcare professional.
The trigger levels for enterococci are set by the National Health and Medical Research Council and are based on the amount of ingestible portions that a swimmer is likely to consume on an annual basis.
Regular swimmers will have a greater exposure and are assumed to ingest a larger amount of water annually.
How can the community help?
Everyone has a role to play in protecting local waterways.
Residents can help by:
- Keeping litter, chemicals and waste out of stormwater drains.
- Picking up pet waste.
- Disposing of waste responsibly.
- Avoiding flushing unsuitable items down toilets and household drains.
- Reporting suspected sewer spills, overflows or water leaks to TasWater.
Anything that enters the stormwater system can eventually make its way to local waterways and beaches.
How will I know when there are changes to water quality advice?
Council will continue to publish updates on its website and work with the Derwent Estuary Program to provide information about recreational water quality monitoring outcomes and investigations at Blackmans Bay Beach.
These FAQs would sit nicely beneath the main explainer and should reduce a lot of the repetitive questions you’ll likely get through Facebook, media enquiries and customer service.