The A39 at Perranarworthal has re-opened.
The main road between Truro and Falmouth has been closed by police due to flooding.
The road is closed from the Devoran roundabout to the Treluswell roundabout. Officers were called after reports that the river had burst its banks and flooded the road.
The road, which runs alongside Restronguet Creek, was also closed on Sunday evening.
Lee Trevena, a chef at the landmark pub on the A39, the Norway Inn, said there was a lot of water on the road. The pub remains open. Highways staff from Cornwall Council are on the scene and diversions are in place.
However the diversion through Ponsanooth is reported to be extremely busy. Police urged drivers to avoid the area if possible.
Cornwall Council said the road will remain closed until at least 9pm.