The mother was found by passersby in a serious condition on the Beechworth-Wodonga Road at Wooragee on Friday afternoon with her joey missing.

Rescuer Chris Lehmann from Kangaloola Wildlife Shelter said despite rushing the koala to "the best vet care on the east coast" in Sydney, the mother died as a result of a suspected gunshot wound.

"We suspect because of the shattering of the bone it was a high-speed, high-velocity impact which is in line with a gunshot wound," he told The Border Mail.

"I spoke to the person who found the joey dead a few days later and her injuries lined up with being on her mum's back and them being shot on the right-hand side.

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"Unfortunately as horrendous as this is, it isn't surprising to us as we know there is the occasional shooting of koalas in the Beechworth area.

"By me speaking to you I hope the person doing this is publicly shamed and we are appealing to the humanity in them.

"I just want to see if they know what they are doing and animal cruelty like this is not an activity someone should be doing to our native wildlife."

Mr Lehmann said wildlife rescuers feared offenders were shooting at the koalas "for fun".

"We had quite a lot of community outrage when we posted on Facebook when we were trying to find the joey and it just goes to show the general population do care about our wildlife," he said.

"But if we see something we need to call it out, this shouldn't be happening and it is really sad that a mother and her joey have died from someone else's cruel actions."

Kanglaloola relies on donations and Mr Lehmann said the organisation was looking for support going into the Christmas period.

"We are always looking for donations - they go a long way to helping to rescue animals," he said.

Donations more than $2 are tax deductible at kangaloolawildlifeshelter.org.au.