Motorists are being warned about a large amount of water on the A47.
Police said road conditions are being badly affected at Castor and that drivers need to take care.
Separately, Lincolnshire Police is warning drivers not to ignore road closure signs.
The force's control room tweeted: "We have had a number of vehicles which have gone through road closures and as a result these vehicles have now become stuck."
A Met Office yellow weather warning for rain has now ended, but heavy rain is forecast in Peterborough this afternoon.