Reservoir Operations Update
Review of July 2026 Operations
Below average monthly rainfall totals were recorded across Grampians storages during July, breaking a run of two consecutive above average rainfall months. The highest rainfall total received was at Lake Bellfield with 91.4 mm (65.8% of the historic monthly average), followed by 76.8 mm recorded at Moora Moora Reservoir (55.3% of the historic monthly average). The lowest monthly rainfall total was received at Taylors Lake with 25.6 mm (60.2% of historic monthly average).
Following two above average rainfall months, catchment conditions remained favourable for the generation of runoff. These conditions supported inflow during the month, with a total of 28,301 ML recorded. This represented 82.2% of the historic monthly average.
Between 1st July and 5th August 2026, the total volume in storage increased from 216,120 ML (38.6%) to 251,050 ML (44.8%), representing a total increase of 34,930 ML (6.2% of total operating capacity). While all storages experienced an increase in volume, Lake Wartook being of particular interest, increased to 17,320 ML (59% of operating capacity).
Although rainfall eased in July, catchment conditions remain wet and primed to respond to future rainfall events. These conditions are likely to support further inflow to storages over the next few months.
Net evaporation from storages totalled -920 ML during July, with monthly rainfall on storages exceeding evaporation for the third consecutive month.
There were no regulated environmental released during July, with unregulated catchment flows continuing in all major river systems.
Consumptive entitlement holders collectively used approximately 775 ML during the month to supply respective urban and rural demands.
August 2026 Operations and Climate Outlook
Below average rainfall in July slowed the volume of inflow to storages during the later part of the month. Even with a slowing down of inflow, harvesting continued from Scrubby Creek in the upper Glenelg Catchment and MacKenzie River and Lower Mt William Creek in the Wimmera River Catchment. These flows are currently being directed to Taylors Lake. Water harvesting to Taylors Lake is expected to negate the need to transfer water from Rocklands Reservoir during the 2026/27 water year. This will create a system saving by avoiding transfer losses associated with this movement of water.
The Bureau of Meteorology (BoM) report climatic conditions reflect a 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 winter and into spring.
The Indian Ocean Dipole (IOD) is currently neutral, with models indicating a positive IOD event is likely during the winter-spring period.
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 (<20%) of receiving median rainfall conditions across the Grampians during August.
Medium-term outlooks indicate a less than 20% chance of rainfall exceeding the median for the August to October period. Daytime temperatures are expected to remain elevated, with the BOM projecting a >80% chance of exceeding median max temperatures for the August to October period.
Reservoirs are projected to hold suitable levels during August 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.