A bushwalker and his dog have stumbled into a mid-water stand-off with a huge kangaroo in WA's South West.

Jackson Vincent encountered the large roo standing in waist-deep water while walking his dog along a creek near Margaret River.

"I ran down and wanted to take a photo of my dog … I turned around and there was a kangaroo sitting in the river," he said.

"He sort of just looked over at us and I started taking photos, and the dog started barking, and then he started coming out of the water and then we realised how big he was.

"He really puffed himself up for me and my dog."

The large male grey kangaroo keeps a close eye on Dharma the dog. ( Supplied: Jackson Vincent and Caters News )

Wildlife biologist Dr Bill Bateman from Curtin University said it was common for kangaroos to head into water to defend themselves against predators such as dogs.

"If they see a dog, and they think that's a potential predator, they'll get into the water in the hope that the dog won't pursue them," he said.

Despite the common image of kangaroos hopping across open Australian landscapes, Dr Bateman said they were also good swimmers.

"When they're in the water they can actually kick alternately with their back legs — so they can do a kind of doggy paddle," he said.

Wildlife biologists say kangaroos are actually very capable swimmers. ( Supplied: Jackson Vincent and Caters News )

Swimming kangaroos

But Dr Bateman said roos did not mind water.

"They have even been recorded running into the sea in some places — sometimes to avoid predators, or dogs — and sometimes because they quite like cooling down."

Mr Vincent said he and his dog Dharma hung around for about 20 minutes to see if the roo would come out of the water.

"She's never really seen a kangaroo before," he said.

"She was pretty energetic at the time — she just wanted to play with this kangaroo, but the kangaroo obviously didn't want to play back."

They left and returned later to find the large western grey kangaroo had also moved on.