The Murray system moves from 15 per cent of high-reliability water shares (HRWS) to 19 per cent HRWS in the latest seasonal determination released by the resource manager for northern Victoria for the 2020/21 season.
The Bullarook system increases from zero per cent HRWS to 5 per cent HRWS.
Seasonal determinations in the Goulburn, Broken, Campaspe and Loddon systems remain unchanged.
Resource manager Mark Bailey said continued dry conditions during July after a dry June had slowed the water availability improvements seen in the previous three months.
"Rainfall in July was below average in the catchment areas," Dr Bailey said.
"After a very dry June, the continued low rainfall meant streamflows slowed appreciably.
"Flows into the major storages in the Goulburn, Broken, Campaspe and Loddon systems in the past fortnight were close to the estimates. That means we didn't pick up more resource for allocation in these systems.
"Flows into the Murray system were enough to increase the seasonal determination by 4 per cent.
"The mid-river storages such as Waranga Basin in the Goulburn system and Lake Victoria in the Murray system are effectively full.
"Flows into Lake Eildon, Lake Hume and Dartmouth Dam plus any supply that is met from catchment flows will define seasonal determination improvements in the Goulburn and Murray systems over the next few months."
Dr Bailey said the latest Bureau of Meterology seasonal outlook still favours above-average rainfall across the catchment ares for the three month period from August to October.
"The outlooks for August and September do not favour wetter or drier conditions over the catchment areas," Dr Bailey said.
"The Bureau's El Nio-Southern Oscillation outlook remains at La Nia watch meaning the chance of a La Nia forming is around 50 per cent in late winter or early spring. La Nia events may support rainfall across southeast Australia."
Dr Bailey advised entitlement holders to use the seasonal determination outlooks and weather information when planning their water needs in 2020/21.