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Fish deaths

What are fish deaths?

Fish death events occur when large numbers of aquatic animals (usually fish, eels, stingrays, prawns or crabs) die in a defined area over a short period. These incidents are reported in Victorian waterways from time to time. 


What are the causes of fish deaths?

While the causes of approximately half of all fish death events are unknown, a lack of dissolved oxygen in the water is the most common known cause. Natural causes can be a common reason for fish deaths particularly during a drought. When lakes, rivers or wetlands dry up, fish often become stranded and die, sometimes in large numbers. When fish are stressed they become more vulnerable to disease and parasite infections. Rapid changes in water temperature can also result in the death of certain species that are unable to regulate their own body temperature. 

Fish deaths from drought conditions 

Image source: Department of Environment and Primary Industries

Human activities can impact water quality and subsequently cause fish deaths. This may occur through the discharging or spilling of potentially harmful substances, or through increased nutrient runoff into our waterways that causes an algal bloom. Algal blooms can cause the water to become depleted of dissolved oxygen leading to fish deaths.


What are the impacts of fish deaths?

Fish deaths may affect aquaculture, can have significant impacts on recreation and social activities, and can result in offensive odours. In marine situations, with changing tides and hungry scavengers, fish deaths are often not visible for very long.


How can fish deaths be managed?

Actions to improve our environment  

The Victorian Government monitors Port Phillip Bay and the rivers and creeks flowing into it. It  measures nutrient algal composition, oxygen levels, toxicants and water clarity, all of which are important in determining aquatic heath. These monitoring programs are used to provide information on the environmental condition of these waterways to help us better manage them. 

The Waterway Incident (Fish Death) Response Guideline is used by the Victorian Government to plan coordinated responses to fish death incidents. Government officers will attend a report of a fish death to facilitate the appropriate response and clean up, if required.                

Informing communities

To help keep Victorians informed, alerts on significant fish death events will be communicated through  this site.


Environmental Citizenship

Through strong environmental partnerships the Victorian government aims to encourage a new sense of environmental citizenship, where individuals, communities, businesses and other organisations take a more active and shared responsibility in efforts to support our environment.

What you can do to help to protect our waterways

One of the main causes of fish deaths is an excess of nutrients in the water leading to algal blooms. Everyone can help reduce the amount of nutrients carried into drainage systems by stormwater and runoff.  

For information on how you can help reduce nutrients refer to: reducing stormwater pollution around the home and business and what can we do round the home about stormwater pollution

If you are interested in knowing more about how you can get involved go to the How you can help page on this website.


Report pollution

Public reports of fish deaths can be made to EPA. If possible, provide the following information when reporting a fish death:

  • location of the incident
  • the name of the waterway
  • whether fish are dead or just affected
  • approximate number of dead fish and whether they are fresh or decomposing
  • whether other animals are affected and the condition of the waterway (flow, colour, odour etc).
If fish deaths or waterway contamination are suspected call EPA’s 24 hour Pollution Hotline (1300 EPA VIC). 

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