Police are investigating extensive damage to a regional golf course caused by chemicals sprayed over at least 17 of the 18 holes just weeks before the club's major annual event.

The damage to the Denmark Country Club greens includes profanities and the words "ha ha" scrawled in the grass.

The vandalism, which is thought to have taken place around New Year's Eve, was only discovered this week.

"Basically, we were playing on the weekend and we noticed quite a few lines coming up around the area and some writing written on the front of the greens," club member Gary Hughes said.

"As the day progressed, we realised that someone's sprayed all the greens and the area walking up to the green; [they've] made a right old mess."

Graham Buckland says the full extent of the damage is still unclear as the chemical takes time to work. ( ABC Great Southern: Aaron Fernandes )

Graham Buckland, the club's operations manager, said the damage was comprehensive but the full extent of it was still unclear as the chemical takes time to work.

"At first it looked like there were just a few lines drawn on some of the greens, maybe with a small sprayer or something like that," he said.

"But there are actually words printed on some of the approaches to some of the greens, some broad spraying on nearly every green, and there's damage out in front of the clubhouse as well."

'Senseless damage'

The damage comes less than six weeks before the club's major annual event, the Denmark Summer Golf Classic, which sold out in just hours.

"We've just got some hard work to get the course back the way it was, because it was looking pristine with all the hard work that's been done around the place and someone's basically come along and ruined it," Mr Hughes said.

"It's disappointment more than anything else.

"You wouldn't imagine that someone would get out there and actually do what they've done."

The vandalism covers the majority of the golf course ( ABC Great Southern: Mark Bennett )

Acting Sergeant Amanda Ball of the Western Australian Police said they were investigating whether the offender may have had a grudge against the club.

"There is some conjecture as to whether or not they've actually played a game of golf on the way through," she said.

"Perhaps held the weedkiller or the spray that they've used in a golf buggy, but all these things are yet to be determined."

A/Sgt Ball said the substantial damage was already visible from the highway.

"Being a Denmark local, we're quite proud of the golf course, particularly as you see it when you drive into town and [at] peak tourist season, lots of people are driving past," she said.

"It's just senseless, senseless damage."