A few lawns - and plenty of passing motorists - have received an unexpected burst of water, after a truck collided with a fire hydrant about 4.30pm Monday.

"A truck's driven over one of the fire hydrants, which has caused the water to flow quite spectacularly I'm imagining from the photos," a Yarra Valley Water spokesperson said.

Yarra Valley crews are at the site, on the corner of Parklands Avenue and Karingal Drive, with the water expected to stop gushing in the next hour or two.

The spokesperson said water would be shut off at about 20 nearby properties for a short time while the problem was fixed.

Meanwhile, locals can pass by for a welcome cool down, or a spot of rainbow hunting.