Review of October 2025 Operations
Above average rainfall totals were recorded across Grampians storages during October. The highest rainfall total received was at Lake Bellfield with 98.2 mm (115% of the historic monthly average), followed by 96.8 mm at Moora Moora Reservoir (113% of the historic monthly average). The lowest monthly rainfall total was received at Lake Toolondo with 55.4 mm (119% of historic monthly average).
Despite above average rainfall being recorded during October, very dry conditions in September limited catchment runoff and inflow to storages. A total of 9,825 ML of inflow was recorded to storages during October, representing 35% of the historic monthly average. Inflow recorded in the July to October period (46,950 ML) represent 31.2% of the historic average for the same period. The July – October period has historically represented the main inflow period for the system, with 75% of all historical inflow recorded during that period.
Between 1st October and 5th November, the total volume in storage increased from 247,030 ML (44.1%) to 253,940 ML (45.3%), representing a total increase of 6,910 ML (1.2% of total operating capacity). Lake Wartook continues to be of particular interest, currently holding 15,030 ML (51%), having shown a modest recovery since July.
Evaporative losses from storage continue to increase throughout spring, with 3.61 GL of net evaporation recorded during October, this is up from the 2.71 GL recorded in September. Losses are expected to increase further throughout summer, with rainfall providing the only offset.
Environmental deliveries continued until late October to the Lower Burnt and Bungalally Creeks, with 446 ML delivered during the resource assessment period. A 12 ML environmental delivery was made to the Mackenzie River downstream of Dad and Dave. Whilst a larger 1,740 ML environmental delivery from Taylors Lake to the Wimmera River also commenced, with delivery continuing through to late November.
Consumptive entitlement holders collectively used approximately 1,412 ML during the month to supply respective urban and rural demands.
November 2025 Operations and Climate Outlook
The Bureau of Meteorology (BoM) indicate that the El Niño-Southern Oscillation (ENSO) is neutral. While there are signs of a possible La Niña developing, they are not of sufficient strength to trigger a La Niña declaration.
Short-term forecasts for the Wimmera-Glenelg headworks area suggest average rainfall conditions for the Grampians over the month.
The Indian Ocean Dipole (IOD) is currently in a strong negative phase, with recent values indicating it will remain negative throughout spring. Accuracy on IOD model predictions is generally limited to one month, making longer term predictions less accurate.
The Southern Annular Mode (SAM) is currently negative as of 25th October 2025. It is expected to return to a neutral value over the next fortnight.
Rainfall outlooks indicate a greater than 50% chance of rainfall exceeding median during November and a 50% chance of rainfall exceeding the median for the December to February period. Daytime temperatures are expected to remain elevated, with the BOM projecting an 75% chance of exceeding median max temperatures for the November to January period. Unless average to above average rainfall conditions develop throughout November, operational decision making will continue to focus on maximising harvesting opportunities and contingency planning for less secure storages.
An 1,800 ML headworks transfer from Lake Bellfield to Lake Fyans will commence in November, with the harvesting of unregulated catchment flows assisting in fulfilling the required transfer volume. This volume is required to ensure an adequate supply of water is held in Lake Fyans to meet expected urban demand for the 2025/26 water year, protect water quality, provide minor environmental flows and support recreation activities.
Reservoirs are projected to hold suitable levels during November for a range of recreational activities. Recreation users are reminded to take care and abide by signage at reservoirs. Please refer to GWMWater’s Reservoir information page for further information on water levels and recreation activities permitted at each reservoir.
There are currently no Blue-Green Algae warnings issued. Information on all current algae warnings, as well as general information on Blue-Green Algae, is available from the GWMWater Algae Warnings webpage.