Fish kills in NSW

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@dpie.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

  1. Blue Green Algal Bloom
    Algal flourish in warm and still conditions, particularly in the absence of high flow
  2. Surface Water Layer
    Warm, high nutrient load from run off.
    Dissolved oxygen by day, depletion overnight
    Limited fish habitat
  3. Deep Water Layer
    Cooler, low light penetration, low dissolved oxygen (hypoxia), Poor fish habitat
  4. Decomposition of organic matter
    Depletes dissolved oxygen
For an accessible explanation of this graphic contact the author Sarah.Fairfull@dpi.nsw.gov.au

De-stratification ("Turn over")

Key

  1. Sudden weather events or small increases in flow
    Can mix the warmer surface water and cooler deep water – essentially breaking down the temperature stratification
  2. 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.
For an accessible explanation of this graphic contact the author Sarah.Fairfull@dpi.nsw.gov.au

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: 1 February 2023 (3pm)

Below are the fish kills that were investigated and confirmed by NSW DPI Fisheries.

There is a current risk of widespread fish kills across parts of NSW. There may be other fish death events that have not been reported directly to DPI Fisheries. To report fish deaths please contact 1800 043 536. This page will be updated as needed to maintain currency.

1 July 2022 - 30 June 2023

Location and date kill observed

Cause and extent

Murray-Darling catchments in NSW

Lake Pamamaroo, near Menindee (23 January)

Report of tens of thousands of dead fish, with species affected including Bony Herring and Carp.

The suspected cause is linked to the fish aggregating at the Pamamaroo inlet regulator attempting to exit the lake. These aggregating fish would have been swimming continuously against high currents from inflows and were unable to exit the lake. This mixed with warmer temperatures in the preceding weeks, followed by a short colder snap likely would have caused the death of already stressed fish.

Ellengerah Creek, near Warren (22 January)Report of 10-100 dead Murray Cod. The suspected cause is attributed to critically low Dissolved Oxygen (DO). The regulator at the top of the creek was closed.  No flow conditions combined with hot and dry weather generated critically low DO.
Reddenville Break, near Gin Gin (19 January)Report of 10s of dead fish, with species affected including Murray Cod and Carp. The suspected cause is a drop in Dissolved Oxygen (DO).
Darling-Baaka River, near Tilpa (17 January)

Report of tens of thousands of dead fish, with species affected including Silver Perch, Bony Herring, Carp, Murray Cod and Golden Perch.

The suspected cause is a drop in Dissolved Oxygen (DO), with a front of poor water quality moving along the Barwon-Darling as floodwaters recede.

Barwon-Darling River, near Bourke 6 January)

Report of thousands of dead fish, species affected include Bony Herring, Murray Cod and Golden Perch; and Yabbies were observed exiting the water.

The suspected cause is a drop in Dissolved Oxygen (DO), with a front of poor water quality moving along the Barwon-Darling as floodwaters recede.

Jemalong Creek, near Gobothery (30 December)

Report of thousands of dead fish, species include Carp and hundreds of Freshwater Crayfish.

The suspected cause is a drop in Dissolved Oxygen (DO), with a front of poor water quality moving through the system as floodwaters recede.

Lower Warrego, near Bourke (19 December)Report of hundreds dead Carp. The suspected cause is stranding following reduction in flow.
Bogan River, near Nyngan (19 December)

Report of thousands dead fish. Species affected included Carp, Goldfish, Gambusia (Mosquito fish) and Yabbies.

The suspected cause is a mixture of some fish becoming stranded and other being affected by deteriorating water quality due to a drop in Dissolved Oxygen (DO). Yabbies were also observed walking upstream towards Nyngan Dam Weir.

Lower Gwydir River, Big Leather area near Moree (5 December).

Report of thousands of dead fish. Species affected included Bony Herring, Golden Perch, Spangled Perch and Carp.

The suspected cause is attributed to critically low dissolved oxygen generated by high rainfall washing organic material into the river. This combined with recent warm weather and a significant reduction in flow as floodwaters recede has also resulted in stranding of some fish in isolated pools and table drains.

Billabong Creek backwater area, upstream from Moulamein (30 November).Report of up to one hundred dead Murray Cod. The suspected cause is attributed to critically low dissolved oxygen generated by high rainfall washing organic material into the river.
Murray River, junction with Darling River, near Wentworth (22 November).Report of two dead Murray Cod and two Carp. Cause is being investigated.
Mildura Marina, Murray River (15-16 November)Report of 1-5 dead fish, species affected include Murray Cod, Golden Perch and Bony Bream. The suspected cause is attributed to critically low Dissolved Oxygen (DO).
Billabong Creek upstream from Moulamein (14 November)Report of 10-20 dead fish. Species affected included Murray Cod. The suspected cause is attributed to critically low dissolved oxygen generated by high rainfall washing organic material into the river.
Murray River (Murray/ Edward-Wakool floodplain) near Goodnight, upstream of Wakool Junction (13 November)Report of hundreds of dead fish. Species affected include Murray Cod, Golden Perch and Silver Perch. The suspected cause is attributed to critically low dissolved oxygen generated by high rainfall washing organic material into the river.
Edward River upstream of Deniliquin (12 November)Report of approximately 20 dead Murray Cod. The suspected cause is attributed to critically low dissolved oxygen generated by high rainfall washing organic material into the river.
Murray River, Murray Downs Marina area near Swan Hill, (12 November)Report of approximately  50-100 dead fish. Species affected are Murray Cod. The suspected cause is attributed to critically low dissolved oxygen generated by high rainfall washing organic material into the river.
Cudgegong River. Windamere Dam spillway (12 to 17 November)Report of approximately 40 to 50 dead Golden Perch located below Windamere Dam spillway. The suspected cause is attributed to the fish being stranded below the spillway.
Murray River at Pental Island, upstream Swan Hill (8 November)Report of approximately 50 dead fish, species affected include Murray Cod. The suspected cause is attributed to critically low dissolved oxygen generated by high rainfall washing organic material into the river.
Billabong Creek near Moulamein (6 November)Report of 3 dead Murray Cod. The suspected cause is attributed to critically low dissolved oxygen generated by high rainfall washing organic material into the river.
Murrumbidgee River near Currawarna, near Wagga Wagga (6 November)Report of 1-10 dead fish. Species affected included Golden Perch and Murray Cod. The suspected cause is attributed to critically low dissolved oxygen generated by high rainfall washing organic material into the river.
Frenchmans Creek upstream Scaddings Bridge, near Wentworth (2 November)Report of 1-10 dead Murray Cod. The suspected cause is attributed to critically low dissolved oxygen generated by high rainfall washing organic material into the creek.
Rufus River near Wentworth, (30 October)Report of 1-5 dead Murray Cod, observed over three days. The suspected cause is attributed to critically low dissolved oxygen generated by high rainfall washing organic material into the Murray River and then pushing that into the Rufus River. High amounts of decaying organic material, combined with recent high temperatures, can significantly reduce Dissolved Oxygen (DO) available which is needed for native fish to breathe and survive.