Review of August 2026 Operations
Close to average monthly rainfall totals were recorded across Grampians storages during August, continuing to maintain saturated catchments. The highest rainfall total received was at Lake Bellfield with 165 mm (126% of the historic monthly average), followed by 93.6 mm recorded at Mt Cole Reservoir (112.8% of the historic monthly average). The lowest monthly rainfall total was received at Toolondo Reservoir with 57.8 mm (99.5% of historic monthly average).
Rainfall received during August was able to maintain saturated catchments, resulting in conditions very conducive to the generation of runoff. These conditions resulted in a total of 42,558 ML of inflow being recorded to headworks storages (excluding Taylors Lake). This represented 82.2% of the historic monthly average.
Between 5th August and 2nd September 2026, the total volume in storage increased from 251,050 ML (44.8%) to 298,450 ML (53.3%), representing a total increase of 47,400 ML (8.5% of total operating capacity).
Catchment conditions remain conducive to produce further inflow to storages in response to future rainfall events. These conditions are likely to persist until rainfall events become less common and daytime temperatures increase.
Net evaporation from storages totalled -2,270 ML during August, with monthly rainfall on storages exceeding evaporation for the fourth consecutive month.
There were no regulated environmental released during August, with unregulated catchment flows continuing in all major river systems.
Consumptive entitlement holders collectively used approximately 784 ML during the month to supply respective urban and rural demands.
September 2026 Operations and Climate Outlook
Catchment conditions will continue to be monitored, with harvesting occurring to storages where possible. Both Taylors Lake and Moora Moora Reservoir are currently being managed to their target filling curves. Rocklands Reservoir continues to increase in volume; with a very high likelihood it will exceed the 116,000 ML trigger volume where a transfer to Toolondo Reservoir can be considered. It is expected this transfer will be considered during September in accordance with the Storage Management Rules.
The Bureau of Meteorology (BoM) report climatic conditions reflect a strong positive El Niño–Southern Oscillation (ENSO) state. International and BoM models forecast a continued warming of the tropical Pacific, resulting in El Niño thresholds persisting throughout spring and into 2027.
The Indian Ocean Dipole (IOD) is currently neutral, with models indicating a positive IOD event may develop during spring.
Positive IOD and ENSO states have historically been observed during drier climatic periods across Australia; however their impact is not certain.
Short-term forecasts for the Wimmera-Glenelg headworks area suggest a below average chance (<35%) of receiving median rainfall conditions across the Grampians during September.
Medium-term outlooks indicate a less than 25% chance of rainfall exceeding the median for the September to November period. Daytime temperatures are expected to remain elevated, with the BOM projecting a >80% chance of exceeding median max temperatures for the September to November period.
Reservoirs are projected to hold suitable levels during September 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 is currently a Blue-Green Algae warning issued for Lake Lonsdale. Information on all current algae warnings, as well as general information on Blue-Green Algae, is available from the GWMWater Algae Warnings webpage.