Are septic systems on the SMBI contaminating the Bay?
Currently, there is no program for systematic testing the waters around each of the Southern Moreton Bay Islands for contamination. This is not a responsibility of council and, if undertaken, falls within the responsibility of the Queensland Department of Environment, Tourism, Science and Innovation (DETSI). I have written to DETSI to ask for advice on any periodical testing they have undertaken or are undertaking around our islands, whether any indications of contamination attributable to the concentration of septic systems on the islands has been found, and whether any systematic testing and monitoring program is proposed.
The good news is that council samples all SMBI swimming enclosures on a fortnightly basis (October – March) and then monthly in the cooler months. While samples often show some e.coli present, this is present in all natural water sources, and there is not a consistent baseline indicative of contamination from island septic systems. If a high count is found the swimming enclosure will be closed. For example, the Russell Island enclosure was only closed once since 2017, and that was in 2018. In 2025 twenty water samples were taken from the Russell Island location with all test results being within the suitable threshold for swimming as per the Healthy Waterways guidelines.
Most high bacterial counts may be attributable to run-off after high rain or a specific event, such as a septic truck leakage. Council and most health agencies offer the same advice regarding swimming post heavy rainfall and that is to avoid swimming in coastal waters for at least one day, and rivers/lakes/estuaries for at least 3 days.
DETSI reports the biggest water quality problems in Moreton Bay are attributable to the 2022 floods. The cumulative impacts of flood events, including the long-term increase in the extent of mud within the bay is also likely contributing to reductions in water quality and direct impacts on key habitats. Water quality data and assessment reports are available on the DETSI website, see Water quality data and assessments | Environment | Department of the Environment, Tourism, Science and Innovation, Queensland