Department testing confirms algal bloom
Released 08 Feb 2013
Water samples taken from the Marbellup catchment, near Elleker west of Albany, show evidence of a large bloom of the algae Nodularia in the same week fish deaths occurred in the waterway.
"The Department of Water attended the scene of the fish kill soon after being notified on Friday 1 February 2013, and took water samples for testing," South Coast regional manager Brett Ward said.
Analysis of the water samples has shown evidence of a Nodularia (blue-green algae) bloom but no microalgae species toxic to fish.
"Our analysis indicates that the algal bloom was in its late stages of decomposition when water samples were taken," Mr Ward said.
"During the decomposition phase of an algal bloom, oxygen is taken up which often depletes the system, as indicated by the very low oxygen levels present at the time of sampling.
"This supports the likely cause of the fish deaths being due to the low oxygen levels as a result of the decomposing bloom.
"Unfortunately no suitable fish samples were available for fish pathology testing due to decomposition, and as a result we cannot conclusively state that lack of oxygen as a result of the bloom was the cause of death.
"In the absence of suitable fish pathology samples, considering the lack of oxygen in the water it could be presumed an algal bloom and related oxygen depletion is the likely cause of the fish kill event."
Approximately 300-400 dead bream and mullet were initially reported to the department in the area above the penstocks at Bridge 45. On attendance department staff counted 100 bream and four mullet.
Reduced rainfall and subsequent reduced flows in 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.
Streamflow for a majority of stations in the region following the 2012 winter was lower than average and this reduced flow, combined with recent hot weather, can lead to water conditions that favour algal blooms.
People are asked to report any fish deaths by ringing the Department of Fisheries Fishwatch number on 1800 815 507.
The Department of Health advises against eating or handling of fish found in these circumstances.
Contact: Peter Collins
Phone: (08) 6364 6848 / 0434 603 441