MDB native fish numbers have ‘continued to decline in recent years’

Native fish populations are in poor to very poor condition across most of the Murray Darling Basin’s catchments, new data has found. See all the latest details.

The number of fish surviving their first year of life has declined across all but four of the Murray Darling Basin’s 23 catchments.

Native fish populations are in poor to very poor condition across 19 of the Murray Darling Basin’s 23 catchments, according to the latest Sustainable Rivers Audit and 2025 Basin Plan Evaluation.

Yet funding for the Basin’s native fish recovery program came to an end on June 30, as the federal government focuses instead on adding to the $243m parcel of water it has purchased over the past 10 months.

The MDBA Authority’s 2025 Basin Plan Evaluation found the ‘just-add-water’ approach to reviving the Murray Darling Basin’s native fish populations had failed to deliver.

“Native fish populations in the Basin have continued to decline in recent years,” the reports, written by the MDB Authority and released on Thursday, concluded.

The MDBA found barriers to fish passage along the Basin’s waterways, cold water pollution from large reservoirs, black water events and a surge in carp numbers had left native fish populations in most catchments in poor condition.

“There have been poor fish breeding and movement outcomes across the Basin, except for estuarine species in the Coorong, Lower Lakes and Murray Mouth. Carp, fish death events and many other factors continue to have an impact on fish populations.”

The number of fish surviving their first year of life to become juveniles - known as recruitment - was rated very poor to poor in all but one of the Southern Basin’s 14 river catchments, from the Mitta Mitta, Kiewa and Murrumbidgee valleys to the Goulburn and Lower Murray.

Northern Basin fish populations fared a little better, with recruitment in three of nine river systems deemed to be fair, including the Darling River, while the rest remain in poor to very poor condition.

The Basin Plan evaluation found carp were the biggest threat to native fish.

“Evidence points to increases in carp breeding, particularly following floodplain inundation and large floods,” the MDBA reported.

Carp are the biggest threat to native fish, with recent floods boosting the pest’s population.

“These breeding events pose a threat to native fish and vegetation. Reporting from Basin governments shows significant increases in carp numbers following flooding in 2022-23.”

“Reporting from Basin governments shows some small positive responses to management of water for the environment at local scales. However, in most cases these responses have not been sufficient to meet Basin-wide targets.”

OTHER BASIN EVALUATIONS

BIRDS

Results vary across the Basin, with states reporting the overall outcomes for species richness have been achieved.

“However, outcomes for abundance have generally not been met, and outcomes for species richness and abundance in the Coorong, a crucial site for migratory shorebirds, have not been maintained,” the evaluation report found.

Bird abundance has not impoved across the abundance, but the diversity of species has increased.

“Although water for the environment is important, other drivers of change for waterbirds in the Basin are likely to include water resource development, climatic conditions and climate change.

“At a site scale, other factors such as loss of habitat, predation, water quality and disease also impact waterbird communities.

“For migratory waterbirds, off-site factors such as the availability of wetlands within and outside Australia and the loss and degradation of mudflats in the Yellow Sea also impact populations.”

VEGETATION

The MDBA found the delivery of water for the environment had largely maintained or improved the condition of woody and non-woody vegetation across the Basin.

“There has been variation over time and across different locations, and there are many areas where constraints limit the delivery of water for the environment to floodplain vegetation,” the authority reported.

Vegetation has improved, but there are areas, such as the Barmah Choke, where high summer flows are killing trees.

WATER QUALITY

Across the Basin the MDBA found there had “generally been good progress in maintaining or limiting declines in water quality, particularly for salinity.

“However, water quality in some areas of the Basin can deteriorate quickly as a result of droughts and floods.”