Fish movement and sensitivity to contaminated mine water

Flowing through the Ranger uranium mine lease and into Kakadu National Park, Magela Creek is home to important populations of native fish species that need to be able to move between the river, floodplain and escarpment country at different times of the year. Fish movement around floodplains during the wet season facilitates the transport of large amounts of nutrients and energy from floodplains to creeks as flood waters recede. This process supports important food sources for Traditional Owners and protects the World Heritage values of the Park.

Weathering of waste rock from the mine releases contaminants, including magnesium sulfate. These contaminants are washed out by the rain and are predicted to move through the local groundwater towards Magela Creek. Depending on the concentration, the magnesium sulfate (a salt) has the potential to affect fish, trees and other ecosystems in and near Magela Creek downstream from the Ranger mine site.

The Ranger uranium mine is due to cease operations by 2021 and this study is leading to better knowledge about how mining waste-related salty plumes may affect ecological processes and connectivity. Researchers are studying fish migrations in the Magela Creek catchment to determine the extent to which magnesium sulfate plumes could interfere with fish movements and related ecological functions and processes. They are also recommending ongoing monitoring and evaluation activities to inform mine closure activities and trial new-generation monitoring equipment and infrastructure.

This project is:

  • investigating fish movement and abundance in Magela Creek and its floodplain at different times of year
  • determining the risks to fish movement from current magnesium sulfate concentrations in Magela Creek from regulated releases of mine tailings water
  • analysing the future risks to fish movement from magnesium sulfate contamination
  • informing mine rehabilitation options and monitoring activities
  • improving our understanding of tropical food web dynamics by using the Magela Creek findings to build on previous work.

Project activities

  • Tag 100 fish with acoustic transmitters to characterise their seasonal movements between the floodplain and refugial billabongs
  • Use imaging sonar to generate near-video-quality images of fish to observe their behaviour and estimate their abundance
  • Deploy underwater video cameras to obtain species-level information on fish abundance and migration
  • Quantify the biomass transported between floodplains and main channel habitats by fish migration
  • Link fish movement data to models of surface and groundwater movement and literature review findings
  • Quantify responses of migrating fish to current approved mine water releases.

Anticipated outputs

  • A conceptual model of how different fish species use the creek based on quantitative information
  • An assessment of the risks to Magela Creek fish species associated with mine waste water
  • A report outlining future ecological risks and options associated with rehabilitation of the Ranger uranium mine site and downstream areas
  • Recommendations for a monitoring program and ongoing assessment of potential impacts to fish communities from the predicted salty water
  • Scientific papers and summary factsheets.

Project update August 2019.

Link to magela creek update


Fieldwork is taking place in Magela Creek, both upstream and downstream from Ranger uranium mine.

Magela and Ranger


This project is being led by Associate Professor David Crook from Charles Darwin University (CDU). A/Prof Crook is being assisted by researchers from CDU and the Supervising Scientist Branch of the Department of Agriculture, Water and the Environment.

This project is due for completion in June 2021.

David Crook, Charles Darwin University
[email protected]


  • An upstream monitoring site in Magela Creek, Kakadu. Photo: Supervising Scientist Branch (Commonwealth of Australia).
  • Researchers will investigate fish migration around the mine site to provide understanding on aquatic impacts. Photo: NESP NAERH.
  • A monitoring site in Magela Creek, Kakadu. Photo: Supervising Scientist Branch (Commonwealth of Australia).
  • Researchers will investigate fish migration around the mine site to provide understanding on aquatic impacts. Photo: NESP NAERH.
  • Researchers will be investigating fish movement to determine mining runoff on fish migration. Photo: NESP NAERH.
  • The researchers will use different methods of tracking fish movement to see the effects of surface groundwater runoff. Photo: NESP NAERH.
  • Gulungul creek floodplain between Baralil and Magela. Photo: Supervising Scientist Branch (Commonwealth of Australia).
  • Magela Creek in Kakadu. Photo: Supervising Scientist Branch (Commonwealth of Australia).