The Department of Biodiversity, Conservation and Attractions (DBCA) advises that elevated levels of harmful algae (Karlodinium spp) have been detected in the Swan River.
The algae can cause a reddish-brown water discolouration and is primarily occurring between Matagarup bridge and Garrett Road bridge in the Swan River.
The algae can produce toxins that can impact fish by damaging their gills and in severe cases, may cause fish deaths.
DBCA officers are continuing to monitor the bloom.
Please do not collect dead fish or allow for dogs to consume dead animals that may appear along the river foreshore.
Whilst this alga is not known to impact human health, the Department of Health recommends that people avoid swimming in water that looks discoloured, murky or smells unpleasant.
If you see dead or sluggish fish in the Swan River, please report to FishWatch on 1800 815 507.