More than 33mm of rain fell in less than two hours late on Tuesday evening.
The deluge left a trail of destruction across towns and villages dotted along the remote north-western region.
Dozens of people were trapped in their cars, livestock was wiped out, and complete roads were destroyed in several hours of freak weather.
Remarkably nobody was seriously hurt or injured.
Calls for the Government to take action on the flooding have been responded to quickly, with the minister responsible for the Office of Public Works arriving in Donegal last night.
Kevin “Boxer” Moran will spend today seeing first-hand the devastation caused by the flooding.
An emergency meeting of the Inishowen Municipal Authority has been called for 11am to discuss a plan of action.
Brendan O’Donnell, senior engineer with Donegal County Council, said it was impossible to plan for the weather pattern which struck the area.
“It was simply unprecedented. I have never seen anything like it before,” he said.
“It’s not something we could have planned for. Sheer volumes of water could simply not get away, with many roads acting as rivers or water conduits.”
Council workers across the peninsula worked throughout the night in a bid to assist in what was an impossible task as heavy rain continued to fall.
The council’s administration staff continued to put out Facebook posts on its account throughout the night in an effort to keep the public informed of developments.
Donegal County Council has also activated its emergency accommodation plan and says no family will be left without accommodation.
At least two bridges were destroyed while others, including Cockhill Bride on the outskirts of Buncrana town, was damaged and had to be temporarily closed.
One van driver had a lucky escape when a huge crater opened up in the middle of the Quigley’s Point to Muff Rd, leaving his vehicle tipping into a huge drop.
Among the worst places hit was the village of Burnfoot. Several families had to be evacuated from their houses as water levels rose.
Businesses such as Floors R Us were left severely damaged.
Owner Karen Doherty, who is originally from Wicklow, was actually filling sandbags and helping to secure businesses in Buncrana when she received the news that her business was under siege.
She has been left devastated after her showroom, which she opened just over two years ago, was destroyed.
“Everything is destroyed but we will start again. We have to. I keep telling myself that other people are worse off than me. I just have to get on with it and I can’t sit around crying about it.
“Somebody could have been seriously hurt or drowned. It’s only materials but we have to start again from the ground up,” she said.
Livestock was also lost in the flood with one witness describing how two donkeys were washed down a country road on the outskirts of Carndonagh.
Huge volumes of crops were destroyed, including fields of corn at the Grianan Estate in Burt, which was recently purchased for €17m.
Holiday-makers coming back through Derry and Belfast Airports could not cross the border into Donegal and reach their homes.
Instead many were forced to remain in hotel lobbies and were yesterday thankful for the kindness shown by hotels such as the Everglades in Derry, which provided them with camp-beds, hot soup, and sandwiches.
Linda Boyle, a mother of two, said she would have had to sleep in her car but for the generosity shown by the hotel on the Waterside.
“I panicked and tried to get a room but it was impossible to get anywhere. I want to thank the staff at that hotel because they were lifesavers.
“I have never been in that hotel in my life but I will make sure I will call into it in future. They showed myself and my children true kindness.”
Several sports club were also left devastated.
Dunree Boxing Club and Cockhill Football Club in Buncrana, as well as Sea Rovers in Malin, were left under several feet of water.
Dunree BC coach Fergal Doyle went to visit the scene yesterday morning.
“The place is just totally destroyed, totally wrecked,” he said as he surveyed the damage.
“Most of our equipment is gone down the river. It’s a disaster. The water was as high as the goalposts on the football field, the owner of the shed was able to tell us.
“We had a treadmill carried 60m away. We have a ring inside that 30 men wouldn’t lift and it was just moved as if it was a football being kicked away. That’s just the force of nature.”
The club only returned to training after the summer on Monday night, with around 25 young boxers in attendance. Last night, the brick walls of the club’s base crumbled under the weight of the gushing tide.
Despite the devastation and the financial cost of rebuilding homes and infrastructure, community heroes emerged from the rubble of the flooding.
Darren Whoriskey spent the entire night around Burnfoot using his tractor to rescue people stranded in their cars and transporting sandbags to shore up homes.
Local senator Padraig Mac Lochlainn said the people of Inishowen have been here before and will rise again against adversity, be that under the devastation caused by freak weather or through carnage on its roads.
“The people of Inishowen are resilient. They will do things for themselves and they will get over this.
“We will sit down and plan a route forward but we do need Government assistance. We cannot simply rely on Donegal County Council because the need here is much greater.
“The people of Inishowen, those who have lost businesses and their homes, need emergency funding and that needs to come directly from funding.”