The reservoir, which holds 59,549 megalitres, supplies both the Ballarat and Geelong areas. and represents 59 per cent of of Ballarat's total local water storage capacity.

The White Swan Reservoir is also at high levels heading into summer, sitting at 86.9 per cent as of this week.

"Across our supply systems, Bullarto, Evansford and Wombat reservoirs, as well as Blackwood Basin and Hepburn Reservoir, have all reached their capacity," Central Highlands Water chief executive Paul O'Donohue said.

"People still need to be wise with their water use as we know over the warmer months there will be a draw down on our reserves."

Mr O'Donohue said based on current Bureau of Meteorology forecasts, the expectation is that Lal Lal will continue to spill well into spring.

SEE THE RESERVOIR SPILLING HERE

It comes as most of Victoria is expected to see a deluge over the next 24 to 48 hours.

Predictions are that up to 40mm could fall in much of the northern, central and western districts into Thursday with the weather bureau issuing a severe weather warning.

While Ballarat was not considered to be in the warning area, regions including Maryborough and Daylesford are, and should expect treacherous conditions in coming days.

The SES has also put out a flood watch warning across the state as the conditions, and the onset of a La Nina even,t mean more rain is likely in coming weeks.

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