Waterways Ireland has said that all of the Shannon is now in flood and that unprecedented levels of water have been recorded.
It is expected that Athlone will be badly hit.
Directors of Services at Westmeath County Council Barry Kehoe said that everything that can be done is being done.
Mr Kehoe said: "We're going continue to protect as best we can areas that are under threat here in the town by providing sandbags and going to continue to work to evacuate people where they need evacuation.
"The army are also going to assist us to access areas outside of the town that are cut off - to the south of the town down at Carrick O'Brien and to the north of the town up at Portlick."