River authorities are monitoring the heavy rains but don't expect Dartmouth Dam to spill just yet

The Murray River's biggest dam is about a metre from the top of the concrete wall and is officially 98.26 full today.

The Murray Darling Basin Authority said it continued to monitor rain inflows but did not expect Dartmouth to spill as it did less than a year ago.

Dartmouth has only spilled five times since it was built in 1979.

One of the startling differences is that three years of La Nina climate influences filled almost all the Murray's storages to the brim and this year an El Nino has been declared by the Bureau of Meteorology.

This current rain "event" has been triggered by forecast low-pressure system dragging moisture from northern NSW into Victoria.

Further downstream, the river's main "operating" dam, the Hume Dam is 89.39pc full.

Much of the heaviest falls from the current rains have been experienced downstream, with a massive 85mm falling in Swan Hill in the six hours from 2am on Wednesday.

River operators have been releasing water from the big storages like Dartmouth and Hume in recent times to create "air space" to cater for the unseasonal inflows.

Communities, landholders, and river users downstream of Dartmouth along the Mitta Mitta River have been encouraged to monitor water levels and check advice on the MDBA website.

BOM has today issued a flood watch for many Victorian streams including the Upper Murray and Mitta Mitta rivers.