Fish kills in NSW 2020-2021
Please report any fish death incidents or observations to the Fishers Watch Phoneline on 1800 043 536
What are fish kills?
Fish kills are defined as a sudden mass mortality of wild fish.
Fish kills can occur at any time although data indicates fish kills are more likely to occur in summer or following sudden changes in temperature.
Recent reports of fish kills are included in the table below and we will update the table as we receive reports.
Some of the key causes of fish kills are outlined in the information below.
Blackwater
Blackwater occurs naturally over time when leaf litter and woody debris build up on the floodplain and then get washed into the river system during a flood. It’s an important part of the aquatic food web as it provides food for insects which feed fish, frogs and other aquatic wildlife.
When there is a prolonged dry period, the leaf litter and organic matter on the floodplain builds up until the next flood event. This can result in a significant amount of organic matter returning to the river with any big flushes of water after prolonged drought, making blackwater events more likely.
Hypoxic blackwater
When there is a lot of organic material washed into the river, its rapid decay can consume dissolved oxygen from the water. If dissolved oxygen drops to very low levels, this can cause ‘hypoxic’ water which can be stressful for native fish and can lead to fish kills.
More information on blackwater can be found on the MDBA website and in this factsheet by DPIE Environment, Energy and Science (NSW DPIE EES).
To notify the department of potential blackwater events email waterqualitydata@industry.nsw.gov.au or to report a fish kill, contact the Fishers Watch Phoneline on 1800 043 536.
Bushfire impacts on native fish
Find information on the impacts of bushfires on native fish.
Stratification?
Stratification is when the surface of the water heats up more than the deeper water. That warmer layer tends to be warm and well-oxygenated compared to the deeper water that is colder and oxygen-depleted.
Thermal stratification
Key
- Blue Green Algal Bloom
Algal flourish in warm and still conditions, particularly in the absence of high flow - Surface Water Layer
Warm, high nutrient load from run off.
Dissolved oxygen by day, depletion overnight
Limited fish habitat - Deep Water Layer
Cooler, low light penetration, low dissolved oxygen (hypoxia), Poor fish habitat - Decomposition of organic matter
Depletes dissolved oxygen
De-stratification ("Turn over")
Key
- Sudden weather events or small increases in flow
Can mix the warmer surface water and cooler deep water – essentially breaking down the temperature stratification - These changes can mix the warmer surface water with cooler deep water
Algal blooms may also be disrupted, potentially increasing decomposition (and further depleting oxygen). This means even at the surface dissolved oxygen levels can become critical, killing fish.
Simple things you can do
- Be on the lookout for any changes in water quality - i.e. changes to the colour or odour of your local waterway and report them to us via the Fishers Watch Phoneline on 1800 043 536.
- Contact us on the phoneline if you observe any dead fish or fish starting to gasp at the water surfaces.
Investigating and reporting
Recent fish death events
Updated: 15 December 2020 (3pm)
- More information on the 2018/19 fish kill events.
- More information on the 2019/20 fish kill events.
1 July 2020 - 30 June 2021
Location and date kill observed | Cause and extent |
|---|---|
Murray Darling catchments in NSW | |
Peel River, Tamworth (7 December) | Report of 10 to 20 dead fish including European Carp and Murray Cod. Cause was episodic rainfall event the preceding weekend that caused short and sharp flow in the river. This can cause a rapid reduction in dissolved oxygen levels due to large volumes of organic material entering the river system. |
