A "grumpy bog monster" has been startling some visitors to the Kakanui area since last week.

The male elephant seal was moulting and was likely to hang around the area for a couple of weeks, Department of Conservation (Doc) biodiversity manager Jim Fyfe said.

"He might be there for a wee while longer," he said.

"Obviously, keep your distance, try not to disturb him. Some of the photos that we've seen he looks a bit of a grumpy bog monster.

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"Just be aware that he's there and keep out of his way, I'd say."

Travis Meyer, of Timaru, came across the elephant seal while fishing and sent Doc photos of it, concerned the animal might be unwell - "not dead, because it was still blinking, but it had seagulls on it".

"He hardly moved, but he was still breathing and then every now and then he would have a cough and all the seagulls would fly away."

Oamaru Doc field ranger Tom Waterhouse said the seal, about 4m long, was about 500m upstream of the Kakanui bridge, and though it was moving from day to day, it would keep to roughly the same area.

Doc had put a wildlife alert sign in place advising people of the animal's presence.

Fyfe said adult males could grow to more than 5m in length.