The Irish Farmers' Association has warned that many homes and thousands of acres of land could be flooded over the coming days unless immediate action is taken by State agencies who are responsible for controlling water levels on the River Shannon.
IFA President Tim Cullinan called on the Office of Public Works and the ESB to release water where possible at weirs on the south of the river over the next 24 hours.
He criticised State agencies for failing to take action on the River Shannon after bad flooding in recent years.
Mr Cullinan's comments come after Met Éireann issued a Status Yellow rainfall warning for Connacht, Longford, Donegal, Clare and Kerry for tomorrow.
The forecaster said 25-40mm of rainfall is expected, with localised flooding likely as the ground is saturated and river levels are elevated following recent heavy rainfall.
The alert is valid from 4am tomorrow until 4am on Thursday.
In Co Roscommon, residents of a rural community are bracing themselves for severe flooding unless urgent remedial action is taken on a turlough flood near their homes.
Flooding near the village of Rahara has already led to the destruction of almost 1,000 acres of land and a wildlife habitat.
Dozens of home and land owners in the area say that unless action is taken on the turlough flood, their properties will be flooded again within weeks and for the second time in four years.
Lough Funshinagh is a type of "disappearing lake" found mostly in limestone areas of Ireland, west of the River Shannon.
Locals say the lough reduced its own levels by up to 20 metres every year in the last 50 years with stretches of dry weather allowing the lake to drain back into the Shannon through what is known locally as a swallow hole in the rock base.
The process can be dramatic in dry weather.
In 1996, around 6,000 fish were killed when the lake drained and "disappeared" in just under a week, but that process has not happened since 2016.
The problem for local residents is acute with more than 1,000 acres of land beside the turlough under water and five homes threatened by flood waters again.
In the aftermath of the 2016 floods, Roscommon County Council and the OPW launched a study to see how the turlough levels could be reduced.
Up to €100,000 was spent on the study but at the end of the process the report claimed there it could cost over €1m to pipe the floodwaters away to the River Shannon and that solution would have to face a cost benefit analysis.
The outcome has angered local people who claim the full extent of the home replacement costs was not considered in the report.
They asking for the OPW to complete a new study and proceed with the proposal to pump away the water.
Levels on Lough Funshinagh have risen to the highest level in three years, and with heavy rainfall predicted this week, residents are bracing themselves for possible flooding.
They are urging the OPW to invest up to €1m to come up with a solution to the problem.