Two University of Otago students had their attempt to surf a fast-flowing Dunedin river cut short after police "firmly recommended" they stop the activity.

Both keen surfers, James Hayers and Toby Hille decided to try their skills on the Water of Leith for the first time this morning.

The river level was raised by ongoing rain that caused Dunedin Civil Defence Emergency Management to evacuate residents living close to the river last night.

University of Otago student Toby Hille rides the current downstream at the river Leith. Photo / Peter Mcintosh, ODT

Police intervened as the surfers walked back upstream, warning them of the risk engaging in the activity posed.

"They firmly recommended that we didn't go back in, just so we're not putting anyone else in danger if they have to come rescue us," said Hille.

He acknowledged that surfing in the Leith posed dangers, such as being knocked unconscious by a rock, but felt he could manage the risk.

"In the ocean there's rocks and boards and stuff as well.

"I was kind of worried about needles and razorblades to be honest, but it was fine — we didn't hurt ourselves."

Hille felt the experiment had gone well, with the water "bumpy, but better than expected", he said.

However, the pair decided against returning to the river following their talk with police.

Senior Sergeant Anthony Bond said people were advised not to enter the flooded river.

Even if people had a feeling of control, a situation could rapidly go wrong.

"It only takes one little knock and then you're washed away."

- by Fiona Ellis, Otago Daily Times