He said that the river was over 20 feet deep at the height of the flood and added that the situation would have been much worse had the 10-hour deluge lasted another hour or two.
"If it rained for another hour the floods would have taken houses and people. It was half-way up my own back door," he said.
IFA president Joe Healy said some farmers were facing ruin because of the losses they had suffered.
"Farmers whose crops and livestock have been devastated by this freak event will have to be part of whatever aid package comes forward from the Government," he said, adding farmers around the country have offered to donate winter fodder.
"In some cases, stock has been lost and in other cases, land and crops are submerged under water. Farm families have been cut off because of damage to roads and bridges," Mr Healy said following a visit to north Donegal.
Agriculture Minister Michael Creed has confirmed that an assessment of losses incurred by farmers in Donegal will take place without delay. Farmers whose lands have been damaged will not be penalised in relation to farm schemes, said Minister Creed.
"I can assure farmers whose land has been flooded and who are concerned about possible consequences in terms of eligibility for payments that a practical approach will be taken in terms of dealing with people who have been victims of these events which were completely outside of their control," Minister Creed said.
"I wish to reaffirm my full support and that of my Department to farmers in the affected areas. We will continue to monitor closely, with input from Teagasc, the effects on agriculture in Donegal," he said.
In the meantime, farmers across the north-west are being forced to house or sell stock, says Teagasc advisor, Tom Coll.
"The ground conditions are atrocious - growth would also be well back. The performance of sheep and cattle is down due to the low dry matter content in the grass," he said.
"It is mainly in the last few days that it has really taken effect.
"Suckler farmers are finding it particularly hard as there is a lot of stock housed," Mr Coll added.
"It is a big worry when you have to dip into fodder stock this early - we've had years in the past where people have had to house stock this early and have never got them back out."
Marts across the north-west have seen a marked increase in the numbers of cattle being sold, with prices for plainer stores back €20-50/hd as a consequence.
Meanwhile, nationally close to half the main harvest remains to be cut.
Merchants estimated that just 40pc of the harvest had been cut by the end of last week. But better conditions since the weekend have given farmers an opportunity to make some sustained progress.
Even so, the IFA said more than half the cereal crop remained to be cut. The farm body claimed that up to 150,000ha (375,000ac) had still to be harvested.
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