Hypoxic blackwater

Stage 1

Water quality monitoring shows indicators within normal range

• All water quality and climatic indicators within normal/tolerable ranges.
• Dissolved oxygen above 4 mg/L at all times. Low risk to aquatic ecosystems.

Stage 2

Water quality monitoring has detected conditions which indicate a potential threat to the aquatic ecosystem.

Any or all of:

• Daily dissolved oxygen levels dropping below 4 mg/L at night/early morning but increasing to above 4 mg/L during the day. Can impact on fish health, but may not result in deaths.
• Forecast rainfall, existing inflows and storage levels indicate increased likelihood of unregulated, overbank flows that will inundate dry floodplain, which is likely to have significant build-up of organic material.

Stage 3

Water quality presents an immediate threat to aquatic ecosystems. Urgent management response is required to avoid fish death or similar event of high ecological implications.

Further deterioration of water quality conditions indicated by any, or all of:

• Local reports of fish gasping at the water surface or deaths. Reports of crayfish leaving the water.
• Dissolved oxygen dropping below 2 mg/L at night/early morning. Water temperature remaining below 25 °C. High risk to aquatic ecosystems. Fish deaths may occur.
• Storage levels at near full capacity. Existing high flows already in the system. Forecast for heavy rain which will result in the inundation of previously dry floodplain.

Stage 4

Water quality is causing significant impact on aquatic ecosystems with potentially catastrophic outcomes – action is required to minimise or mitigate against further mass fish death.

• Confirmed reports of widespread fish deaths.
• Dissolved oxygen level remaining below 2 mg/L and water temperature above 25°C. Very high risk to aquatic ecosystems, and fish deaths occurring.
• Weather forecasts indicate poor water quality is likely to deteriorate further