Henry Rooney says more than 20 years of work on his farm has been "washed away overnight".
The gutted Ashburton farmer today told 1 NEWS the Canterbury floods, meant to be a one in 100-year event, had been "devastating".
"You can't stop it, you can't do anything about it. You've just got to sit back and watch and see what happens," he said.
"Over 90 per cent of the farm is under water now ... it's just gone really.
"I've seen flooding here before but nothing that's blown the banks. I don't think anything would have stopped that amount of rain, it's just relentless.
"I've seen it happen on TV before but I never thought it would happen here, well, not to this degree anyway, but here we are."
Rooney also said he hadn't been able to sleep the past two nights due to the river "roaring at night".
"Every couple of hours you're going out to check the house isn't under water and stuff," he added.
"It's just been really, like you say, soul destroying," he told 1 NEWS reporter Lisa Davies.
"I suppose, what can you do? Just got to plod along and do day-by-day.
"It sucks, it just sucks."
Canterbury residents this morning woke to an ongoing state of emergency.
It comes after heavy rain pounded the region yesterday, forcing thousands of people to evacuate.
But the region is still experiencing heavy rain, with Rooney saying the overflowing river which swallowed his second-generation farm is still rising.
"Now it's just all under water, it'd be alright if cows ate water but they don't," he said.
"Can't do anything about it, just got to deal with it and carry on."
For continuing live updates on the situation in Canterbury, go here.