Concerns raised after fish kill in Lower Vasse River as authorities investigate water quality

Concerns have been raised after dead fish were discovered in the Lower Vasse River earlier this month, prompting an investigation by environmental authorities.

Department of Water and Environmental Regulation officers responded to the incident on January 19 after a small number of sea mullet were found dead along a stretch of the river between the Camilleri Street bridge and an area about 50m south of the City of Busselton office carpark.

The fish were seen floating in the water and along the shoreline.

The exact cause of the fish deaths has not yet been confirmed.

Data from water quality loggers in the river recorded low dissolved oxygen levels for two days prior to the incident, which may have contributed to the event.

The City of Busselton did not respond to questions about concerns for other areas of the Vasse River and fish species or what killed the sea mullet, and directed all queries to DWER.

DWER has collected water quality and phytoplankton samples for further analysis and said low oxygen levels were a known cause of fish kills, particularly during warmer months and in waterways affected by elevated nutrient levels or algal growth.

While the Lower Vasse River typically experiences phytoplankton blooms each summer, fish kill events in the system are considered uncommon.

DWER said at this stage the incident appeared to be localised, with no broader environmental impacts identified.

Last October, Vasse MLA Libby Mettam took aim at the management of the Vasse River in Parliament, saying it had been turned into a “dead zone”.

“They (the city) have been challenged by a lack of funding and the complex bureaucratic management structure of State Government agencies that oversee this project,” she said.

“The areas excavated are much too small to alleviate the algal blooms or have a positive impact on water quality. The Lower Vasse, as it stands, remains a cesspit without any foreseeable medium-term solution.”

DWER said it continued to work closely with the City of Busselton to monitor conditions and determine if more response actions were needed.

Anyone who sees further fish deaths or has concerns is encouraged to report them to DPIRD Fish Watch on 1800 815 507.