River levels are rising on the Lower River Ribble and River Darwen.
A flood alert is in force from the Environment Agency.
Update: During Monday morning all flood alerts and warnings were withdrawn
It covers the area from the rail bridges in Avenham Park up to the Tickled Trout, Samlesbury and Brockholes.
Flooding is also possible around the Captiol Centre in Walton-le-Dale.
Savick Brook in Fulwood is also being monitored, along with Eaves Brook and Sharoe Brook.
The Environment Agency says flooding could occur between 9pm on Sunday (28 July) and 9am on Monday (29 July).
A statement from the Environment Agency said: “Our incident response staff are checking defences and clearing weed screens. Please avoid using low lying footpaths near local watercourses which may be flooded.”
Read more: Major flood defences plan for the River Ribble is showcased
In Leyland, a flood warning, the second-highest flood warning level, is in force around the River Lostock.
You can see flood alerts and warnings on the Environment Agency website.
A yellow weather warning of heavy rain remains in force from the Met Office and Preston has seen constant rain throughout Saturday and Sunday.
Read more: Police forced to close Preston Docks junction due to flooding