Department of Water and Environmental Regulation staff (DWER) have responded to reports of dead fish in the Lower Vasse River on Monday 19 January.
DWER officers attending the site reported and observed a small number of sea mullet had died between the Camilleri Street bridge extending upstream to 50 metres south of the City of Busselton office car park.
Fish were observed both along the shoreline and floating in the river, however, there were no fish suitable for pathology analysis. The City of Busselton are planning to remove the dead fish.
The cause of the fish deaths is still unknown, however water quality loggers in the river showed low dissolved oxygen for two days prior which may have contributed.
Water quality and phytoplankton samples have been collected for analysis.
Low oxygen events are a known cause of fish kills in waterways, particularly during warmer months and in systems experiencing elevated nutrient levels or algal growth.
Results from the water quality analysis will help confirm the contributing factors.
The Lower Vasse River experiences phytoplankton blooms each summer; however fish kill events are uncommon.
At this stage, the incident appears to be localised, and no wider impacts have been identified.
DWER is continuing to work closely with the City of Busselton to monitor the situation and provide advice on any further response actions that may be required.
Anyone who observes further fish deaths or has concerns is encouraged to report them to the DPIRD Fish Watch on 1800 815 507.
