The Department of Water is investigating a report of a possible fish kill along the Serpentine River south of Lake Amarillo.
Numbers are unknown but samples of around 20 Black Bream brought in by a member of the public have been given to the Department of Fisheries to undertake pathology tests.
Department of Water staff have undertaken water quality sampling in the vicinity of the reported area and searched for further evidence of the incident.
Department of Water Kwinana Peel operations manager Alan Cook said the area of the report is highly influenced by tidal movements and notoriously difficult to access except under certain conditions.
Several kilometres immediately upstream and downstream of the report were inspected and no dead fish were located.
Mr Cook said fish kills at this time of the year are commonly related to low dissolved oxygen, caused by high temperatures and exacerbated following summer rains due to input of nutrients and organic material. These conditions also favour algal blooms, which can be implicated with fish kills.
Contact with dead fish should be avoided and the Department of Health advises against eating or handling of fish found in these circumstances.
People are asked to report any fish kill events so that the department can investigate.
Fish kill incidents can be reported to the Department of Water Kwinana-Peel regional office on 9550 4200 or by ringing the Department of Fisheries Fishwatch number on 1800 815 507.
Media contact: Peter Collins (08) 6364 6848 / 0434 603 441