A farmer who had allowed people to visit swimming areas on his land has shut access off.

A northern Southland farmer has padlocked a gate leading to a popular swimming hole after finding soiled nappies on the riverbank.

Waikaia farmer Ray Dickson took the action to cut access to a spot known locally as Roly's Rock, at the edge of the popular holiday town, after finding nappies in grass on the riverbank on December 29.

"It really p..... me off.

Rachael Kelly Ray Dickson at a swimming hole known as Roly's Rock. He padlocked a gate that gave access to the area after finding soiled nappies on the riverbank.

"The thing that p..... me off is all the people that have had to miss out because of other people's stupidity."

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The swimming hole on the Waikaia River was popular with locals and holiday makers because it was close to town and, until now, people could drive to it through Dickson's paddocks, which he has been farming for 40 years.

Rachael Kelly A Waikaia farmer has padlocked access to a popular swimming hole after finding soiled nappies and rubbish on the river bank.

People wanting to take a dip could still walk through the paddocks or access the river from the other side.

"Ninety nine percent of people are bloody wonderful. The local kids and the camping ground kids come down here and they all take their rubbish away.

"Glass gets left on the beach sometimes but I don't have to pick up rubbish down here at all really. People are pretty good."

The nappies were left in cutty grass on the riverbank.

"It must have been deliberate because you don't lie your baby down in cutty grass to change it do you? They were kind of concealed there, so it wasn't an accident.

"You just get to the end of your tether ... People seem to think it's their right to go there."

Dickson asked the local shop to put a post on its social media page advising why the gate was locked, and he had made a sign to put on the gate.

Locals posted on the page in support of his actions, and one said they had also picked up beer bottles from another swimming hole nearby.

He said no-one had come forward to apologise.

"I certainly hope it's not a local. I don't think it will be, but I really hope it's not."

The town didn't have problems with freedom campers like other areas and the Southland District Council had designated a place for them to park at the town's Recreation Centre, he said.

Dickson planned to reopen the gate and hoped the offender had learnt their lesson.

"Whoever it was has ruined it for everyone else."