Water testing completed in response to Keralup fish deaths
Released 25 Feb 2013
Water samples taken from the Serpentine River in Keralup have found evidence of a naturally occurring algal species that can be toxic to fish.
The species was found in water samples taken by the Department of Water in response to a report of fish deaths in the river.
"Following information from the Department of Fisheries about dead fish in the river, Department of Water staff attended the scene along the river bed in Keralup and collected water samples," Department of Water, Water Science Branch manager Malcolm Robb said.
Mr Robb said the dominant algal species identified by the department's sampling was the potentially fish toxic flagellate Heterosigma akashiwo.
"Unfortunately no suitable fish samples were available for fish pathology testing due to decomposition, so we cannot state conclusively what killed the fish," he said.
He said this species of algae had been found in high concentrations in the past in the lower reaches of the Serpentine river, although extensive blooms of blue green algae were also observed along much of the Serpentine River adjacent to Keralup.
"At the time of sampling oxygen and pH levels were relatively normal.
"While there is the possibility this species of algae played a part in the fish deaths, the general condition of the river covered by blue-green algae and the observed appearance of low oxygen in the bottom waters suggest that low oxygen conditions contributed to the deaths."
Low rainfall and seasonal low flows in the state's south west inland waterways over summer months increases the potential for algal blooms, with the risk of increased growth in river pools as they dry and stagnate, Mr Robb said.
"Reduced river flow can lead to less dilution of nutrients and in algal bloom prone areas this may lead to increased algal growth, or a shift in the type of algae, sometimes to a species like this which is more toxic to fish. vMr Robb said most fish kills most commonly occur from a lack of oxygen in the water column caused by the breakdown of organic matter and not necessarily as a result of algal toxicity.
The area in which the dead fish were found was not accessible to the public.
The Department of Health advises against eating or handling fish found in these circumstances.
People are asked to report any fish deaths by ringing the Department of Fisheries Fishwatch number on 1800 815 507.
Contact: Peter Collins
Phone: (08) 6364 6848 / 0434 603 441