The Environment Agency has issued the warning this afternoon (Wednesday) as heavy rainfall has been seen in the River Bain catchment area over the last 24 hours.
This means that river levels are now rising, which may lead to flooding of low lying land and roads close to the river from this evening onwards.
The areas likely to be affected according to the map are the villages around the river, including Baumber, Belchford, Tetford, Woodhall Spa, Mareham le Fen, Scamblesby, and northwards Welton le Wold and Ludford Magna may also be affected.
A spokesman said: “We expect the river to remain high throughout the next few days.
"Our forecasts indicate that flooding to properties isn't likely and therefore flood warnings are not expected to be issued.
"We are constantly monitoring river levels, and have staff in the field checking for blockages and clearing weedscreens.
"Please avoid using low lying footpaths near local watercourses and plan driving routes to avoid low lying roads near rivers, which may be flooded.”
An amber flood warning means that flooding is possible, and residents should be prepared.
If you haven’t already done so, you should, sign up for flood warnings and keep up to date with the latest flood risk situation by calling Floodline on 0345 988 1188 or follow @EnvAgency on Twitter for the latest flood updates