Water quality and ecological health - Fish kills

Fish kills 

Fish kills involve a sudden and significant death of fish and/or other aquatic animals such as crabs and marron, and are characterised by a large number of aquatic animals dying during a short period of time, often in a defined area. The Swan Canning Riverpark can experience fish kill events of varying intensity.

One of the most common factors behind fish deaths in the Swan Canning Riverpark is oxygen depletion. Evidence suggests that fish will move away from low oxygen areas, however hypoxic conditions (dissolved oxygen of less than 2mg/L) will put fish under stress, and anoxic (no oxygen) waters will result in fish deaths, particularly if the change to anoxic conditions is very sudden. Low oxygen can be caused by a number of factors.

Other causes of fish death include:

• some species of algae which are harmful to fish, such as the dinoflagellate Karlodinium veneficum which can release toxins under certain conditions. Other species of algae affect fish by coating their gills with a mucous-like substance that prevents fish from extracting oxygen from the water
• contaminants
• changes in pH due to acid drainage water arising from earthworks in areas with acid sulphate soils
• fishers leaving unwanted fish on shorelines

Responding to fish kills

When there is a fish kill in the Swan Canning Riverpark, Parks and Wildlife forms an Incident Management Team and follows Statewide response procedures established by the departments of Water and Fisheries.

How you can help

Parks and Wildlife encourages the public to report dead or sluggish fish in the Swan Canning Riverpark on 9278 0900 or after hours on 9278 0981. Provide as much information as possible including:

• your name, address and contact details (caller can remain anonymous if preferred)
• exact location of the fish kill and easiest access point
• date and time you observed the event
• estimate of the number of fish affected and their state (ie: dead, dying, alive, very decayed, gasping at the surface, lesions etc.)
• approximate size and species of fish affected
• whether there are surface scums present (eg oil slicks, coloured water, rubbish) or odours in the vicinity
• any unusual activity that may have contributed to the event (eg dumping of chemicals or recent spraying)

For your safety, you should never consume fish in the vicinity of a fish kill or come into contact with affected fish or water. Do not collect fish in these circumstances.