What is going on?

While rainfall for the 2022-2023 year was above average and may have had positive influence on the catchment, the poor grade results from a changing climate where lower rainfall and higher temperatures result in less water available, along with a large number of dams in the hills reducing the amount of water entering the rivers.

Most of the rain in this catchment falls in the hills where many larger dams exist that were constructed prior to government regulation of the water resource. Capture of surface water by dams prevents it from moving downstream which changes the pattern and amount of water flowing through the catchment. It causes increased salinity and stress on aquatic organisms, decreased biodiversity and a restricted amount of time for breeding of fish and other aquatic organisms.

Groundwater in the lower plains areas is also recharged from water flowing down from the hills. Surface water and groundwater are required to refresh and maintain important permanent pools. Without regular water supply they become increasing shallow, saline and low in in dissolved oxygen, making them less suitable as a dry-season refuge for aquatic life.

These permanent pools are a critical habitat for the river blackfish. Unfortunately, this fish species has been so badly impacted that there is no longer a breeding population present and the species is considered functionally extinct in the Marne Saunders catchment.

What can we do?

Dam owners can participate in the Flows for the Future program by installing low flow bypasses.

Dams capture all new season autumn flows until full and then spill over. This significantly shortens the flow season for natural water courses. Low flow bypasses work by passing small volumes of water that flow after minor rainfall events through a device that bypasses the dam. Larger rainfall events that result in higher volumes of water flow enter the dam.

This has a small impact on the total volume of water that dams capture but has a big benefit for watercourse health.

Community members can get involved in citizen science projects such as Waterwatch, Waterbug Bioblitzes, microbat monitoring, and iSPYthon. These projects collect data about water health and biodiversity in the catchment which could be used in future report cards. People can also connect with restoration programs led by the Murraylands and Riverland Landscape Board, local environmental work and support by Mid Murray Landcare SA, and other community initiatives that develop.

All community members can participate in the upcoming water allocation plan review process to design future water policy that supports a sustainable future for the catchment.

The seasonal nature of the Marne Saunders river systems means that isolated permanent water pools become important refuges for aquatic life during the dry season, while other native animals use the pools as drinking water in dry times.

The condition of permanent water pools as aquatic habitats is indicated by 3 important water quality measures- dissolved oxygen (DO), salinity (conductivity), and pH. Grades are assigned using thresholds based on the requirements of 3 priority native fish species that have different sensitivities to declining water quality (from more to less sensitive) - river blackfish, obscure Galaxias and carp gudgeon.

Permanent pools showing stress typically have low dissolved oxygen (DO) levels, high salinity, and low suitability for fish populations.

Fish monitoring focused on evaluating abundance, species richness, age classes of fish sampled, and the presence of sensitive species. Data was collected for native and introduced fish species.

For the 2023 year the fish indicator highlighted:

• Sites in the Upper Marne sub-catchment showed strong native fish populations, with high numbers of obscure Galaxias and carp gudgeon, and minimal presence of introduced species. This suggests relatively good water quality and habitat conditions and is likely to be a short-term breeding response by the fish due to the wetter than average 2022-2023 year.
• In the Lower Marne sub-catchment, which also includes a survey from the wetland at the mouth of the Marne, there was a higher prevalence of introduced species such as eastern Gambusia and common carp, leading to lower scores for fish community health.
• Lower Saunders and North Rhine sub-catchments showed the poorest results, with low native species richness and high numbers of introduced species. These findings highlight the need for habitat restoration efforts and improved water flow in these regions to support native fish populations.
• Sadly, it is clear from the ongoing assessments that the population of river blackfish population that was living in the springs in the lower catchment has not survived and is now considered functionally extinct from the Marne River.

Macroinvertebrates (waterbugs) are reliable and commonly used indicators of river health due to their sensitive to changes in water quality, habitat structure, and flow regimes.

The macroinvertebrate assessment of the Marne Saunders catchment reveals a generally degraded condition, with poor community diversity and an overall low abundance of flow-sensitive species. Communities are dominated by species capable of surviving in harsh, intermittent flow conditions and higher salinity levels, such as non-biting midges and diving beetles. Only some pools in the Upper Marne sub-catchment were graded as ‘Fair’ due to higher macroinvertebrate diversity and more stable populations of flow-sensitive species.

For a more detailed analysis please read the Report Card Technical Report.