A large seal found on a western Victoria dairy farm has been euthanised after a wildlife assessment determined the elderly mammal could no longer "forage and live naturally in the wild".

Melbourne Zoo marine and veterinary teams and Parks Victoria wildlife authorities attended the farm on Thursday afternoon to assess and determine the next steps in the care of the seal.

Head veterinarian Michael Lynch said Melbourne Zoo was contacted after the large adult Australian fur seal "failed to find a way back to the open ocean along the same path it used to arrive at the farm".

The large wayward seal attracted national attention as it made itself at home at the Simpson dairy farm, 30 minutes away from the nearest beach, on Sunday.

Dr Lynch said on assessment the seal was "found to be elderly, and suffering from blindness in one eye and dental fractures".

"It was determined that euthanasia was the kindest welfare outcome as the seal would have been unable to forage and live naturally in the wild," Dr Lynch said.

He said a necropsy would be conducted in the coming days.

He asked anyone who sees wildlife in distress or needing assistance can contact the Melbourne Zoo Marine Response Unit on 1300 245 678.

Earlier: Thursday, 1pm

A Melbourne Zoo team has travelled to a western Victorian dairy farm to rescue a 160-kilogram seal found wandering around a boggy farm paddock.

The mammoth effort to lift and remove the mammal is being undertaken by zoo and Parks Victoria crews on Thursday afternoon.

The large wayward seal attracted national attention as it made itself at home at the Simpson dairy farm, 30 minutes away from the nearest beach.

The farm owners, Karli and Brad McGee, were shocked to spot the seal in a paddock in the inland rural bush setting on Sunday.

The unexpected visitor is estimated to weigh between 150 and 160 kilograms with his size and wet, boggy paddocks expected to prove challenging in the well-planned rescue.

Mrs McGee said the male seal had since moved to neighbouring properties, including her parents farm, through paddocks, creeks and laneways, usually reserved for dairy cows.

She said the seal had travelled about four kilometres on land, across the length their 400-acre property and her dad's neighbouring farm, since his arrival.

"He travelled from one side (of our farm) to the other and then yesterday he travelled across my dad's whole farm and went over the back of his farm and gone in the back," Mrs McGee said. "He's gone on grass he's not even going through creeks, he's going inland.

"It looks like a lot of effort when you watch him but he seems to move fast enough if he wants to."

The seal disappeared from view on Wednesday with slide markings across the farms helping to highlight its movements.

Prior to the rescue Mrs McGee said it would take a few people to get him out and Parks Victoria were on site watching him ahead of the Melbourne crew's arrival.

"He's moving fast so they're just trying to keep track of him," Mrs McGee said.

"It's on someone else's property now and they're hopefully going to get it out but it's going to be gone today (Thursday).

"They're going to check him out and he's either going to go back to the zoo or be released back into the ocean."

She said her mum had been keeping in touch with zoo staff via regular phone calls, photos and videos for condition updates throughout the week.

"I think he's looking for food now," Mrs McGee said. "He looks pretty good. He looks alright, I think he's just exhausted from trying to travel in land."

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