The roo was spotted stuck and shivering in the cold water about 7am on September 17.

Penelope Twemlow said she saw the kangaroo try and fight a man on bike before ending up in the lake.

"I saw a kangaroo fighting, for want of a better word, a gentleman on a bicycle," she said.

"That gentleman had the bike in between him and the kangaroo to try and defend himself, and the minute he tried to get away the kangaroo went after him again," Ms Twemlow said.

"In the kerfuffle, the kangaroo ended up in Lake Burley Griffin."

Ms Twemlow said the kangaroo "was visibly in shock and shaking quite badly" before bystanders tried to take it out of the lake.

"I just thought we have to get the poor thing out of the water, and then try to get it onto dry land so it can do what it needs to do," she said.

After being pulled onto a grassy patch, the kangaroo "started to essentially fight one of the gentlemen again and then jumped straight back in the water and swam out to the middle of Lake Burley Griffin," she said.

The kangaroo was eventually taken onto dry land, and the rescue video went viral across the world.

However, ACT Parks and Conservation said a veterinarian had found the roo was too sick to be saved after visiting the animal at Lake Burley Griffin.

"The government veterinarian examined the kangaroo and found the animal to be in poor physical condition. Given significant concerns for the kangaroo's welfare, the animal was euthanised," a spokesperson said.

"Capture myopathy, or muscle damage resulting from extreme exertion or stress, is always a primary consideration in any rescue of a kangaroo.

"Several factors contributed to the welfare concerns for this kangaroo, including the poor symptoms the animal was showing, the location where the animal was found, and the cold, windy weather."

They said saving wild animals should be left to professionals.

"Due to safety concerns, to both the animal and the public, we ask that the community do not attempt a rescue themselves," they said.

"Please give the animal space and keep an eye on them from a distance - maintain enough room for the animal to leave the area."

If you see an injured or distressed animal, call Access Canberra on 13 22 81 or ACT Wildlife on 0432 300 033.

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