The Environment Agency is facing a furious backlash as communities in the south west already hit by flooding were warned that more could be on the way.
Environment Secretary Owen Paterson may also face a frosty reception during a visit to the region to hold crisis talks with farmers and local authorities.
Yesterday, farmers held a demonstration against the Environment Agency, accusing it of failing to dredge local rivers.
And today a local Tory MP hit out at the agency, blaming it for exacerbating problems on the Somerset Levels, where some communities have been inundated with flooding since Christmas.
Bridgwater and West Somerset MP Ian Liddell-Grainger told the BBC Radio 4 Today programme: "Once it's dredged we can then maintain it but the Environment Agency has to stop this mucking around and get on with it."
He dismissed as "pathetic" the Environment Agency's claims that the rain would have overwhelmed the river system even if it had dredged the waterways.
"It is an absolutely ridiculous excuse," he said. "This never flooded to this level ever in living memory, and we've got people who have been here for a long time. If you look back into the mists of time you don't have this.
"What galls my constituents... is they found £31 million to build a bird sanctuary at the mouth of the Parrett river, yet they cannot and will not find £5 million to dredge this river."
Responding to the cricitism, David Cameron defended the agency.
He said: "I think the Environment Agency has done excellent work on helping to deal with the flooding and helping with communities.
"I have, in my own constituency, worked with them very closely.
"I think a couple of years ago there was a sense that they were very anti-dredging, very anti-action on particular rivers and streams.
"I think they have changed their attitude on that front but I will listen very carefully to what Ian has to say about these specific rivers. I know Owen Paterson is going to Somerset and is going to meet with the MPs.
"Obviously the Environment Agency has to listen to these concerns - you do get quite widespread concerns that river levels have risen.
"We have got to address those and give some clear answers."
The Met Office said the counties of Hampshire, Dorset and Somerset remain at medium risk of flooding as another day or rain hits the regions.
Meanwhile, snow will fall across high ground throughout the UK, particularly across Wales, Scotland and northern England, with some hail storms and thunder predicted.
Temperatures will fall to around freezing, resulting in a risk of icy stretches on roads and the potential for travel disruption, the Met Office added.
The Environment Agency has issued more than 140 flood alerts and 10 more serious flood warnings in the south west, which mean flooding is expected and immediate action is required.
Somerset County Council has declared a "major incident" after large parts of the county remain under water.
Council leaders, the emergency services and government agencies who make up the Local Resilience forum on flooding met last night to discuss the flooding crisis.
The group said that people at risk of flooding were visited over the weekend by either the emergency services, local authorities or local utility companies.
Avon and Somerset Police have launched a police boat to reach flood-hit homes in Muchelney on the Somerset Levels.
The team gave fire prevention and health and safety advice to residents who have been affected by the floods.
Many communities are still coming to terms with the flooding that hit Somerset at the beginning of January and now face further problems.
Somerset County Council deputy chief executive Pat Flaherty said: "Our priority has to be to keep people safe.
"We are doing everything we can to do this and we believe that declaring a major incident shows just how urgent the situation is for many of our residents and communities.
"The reason we are taking this action is the long-term nature of the issues we are facing and to enable a consistent approach to the way that we deal with them."