An expert on surf rage has called an incident where two were shot at as "really extreme".

Waikato Police are investigating after two people were shot at while surfing off Te Maika peak last Thursday - bullets hitting as close as 2m away.

Police say someone had taken exception to "strangers" using "their" water.

The shots came from surrounding bush land, which was commonly used for hunting, police says.

Jhan Galava is doing a PhD on surf rage.

"It's the first time I've heard of anyone actually being shot at," he told RNZ's Jesse Mulligan.

"That's really extreme.

"In all the research I've done and places I've surfed there has never been anything like that.

"There are urban legends in Hawaii, stories of guns being wielded but never fired."

There were a number of causes of surf rage, which included but were not limited to, intergenerationally learned violence, low coping skills, notions of local entitlement and competition.

"One of the themes is protection. They want to protect their surf break. They see it as a scarce resource.

"Local surfers are really passionate and they have a strong connection to where they surf and they feel they have the rights and entitlements to that place.

"They want the best waves as they've done the time there."

Common reactions to outsider surfers was to abuse, splash or ram them with their boards.

"There are lots of ways in which they do that."

His research revealed there was little desire from surfers to change tactics of intimidation to protect their surf spots.

"They're quite happy with their ways of resolving it. If you've really intimidated someone and they don't come back, that's a really positive outcome for them."

He said it was "a really small percentage of surfers" who participated in intimidation tactics and that scenes around the world were "all pretty much the same".

"[But] locals set their own protocols, their own etiquette."

Mr Galava, a sports psychologist, has taken a break from his research into surf rage to work with a number of sporting organisations, including The Blues and New Zealand surfers hoping to compete at the next Olympic Games.