With prolonged rainfall expected over the next two days on top of already high water levels, warnings are in place from the Environment Agency for the River Witham and associated Fens from Washingborough, to Metheringham, to Chapel Hill and Boston.
The warning means flooding is expected and immediate action is required.
The agency said: “Heavy rain fell over the River Witham catchment over the weekend and further heavy rainfall is forecast for tomorrow, Tuesday. We still expect properties along the River Witham and associated Fens to be affected.
“Low lying properties near the river are most at risk. River levels are expected to remain high throughout this week.
“Stay safe and be aware of your local surroundings. Avoid contact with flood water, riverside paths and river embankments.
“Our staff are out in the area to check the flood defences, clear blockages, operate our assets and assist the emergency services and council. We are closely monitoring the situation.”
An amber flood alert across the rest of the area is also in place asking people to be prepared for possible flooding in villages bordering other minor water courses such as the South Forty Foot Drain and tributaries of the lower Witham from Blankney to Sleaford.
Officials said: “Our forecasts indicate that flooding to properties is not likely and therefore flood warnings are not expected to be issued. Please avoid using low lying footpaths near local watercourses and plan driving routes to avoid low lying roads near rivers, which may be flooded.”