Busselton wildlife rescue organisation FAWNA president Suzi Strapp said its volunteers were "exhausted" and needed more support from the Department of Biodiversity, Conservation and Attractions.
Ms Strapp said wildlife rehabilitators and vets in the region were "inundated" with animals suffering from heat stress and burns.
"We have formally reached out to [department] for assistance and guidance as we are overwhelmed, exhausted and have simply run out of appropriate housing," Ms Strapp said.
"A reply, which arrived weeks later, downplayed our concerns and rather than responding to our requests offered letters of support for grant applications."
A department spokesperson said wildlife rehabilitation had always been undertaken by volunteers in WA, supported by local veterinarians where possible.
"[The department] does not employ staff to collect and rehabilitate native fauna and is greatly appreciative of the great work fauna rehabilitators do and will continue to support grant applications to assist with providing them with more resources to maintain the important role they undertake," they said.
Ms Strapp told the Mail about a particular incident which occurred on March 11 where a Busselton resident found a "seemingly immobile" possum on the ground in their front yard.
Ms Strapp said the resident claimed they first received advice to leave the animal alone because possums "often liked to lie on the ground on hot days".
However, the next day the resident checked on the possum that hadn't moved overnight.
Ms Strapp said the resident then called FAWNA and was told to take the possum to a vet.
"On assessment, the vet found the animal had severe burns to paws, tail, pouch and had grazing on its back, possibly from being caught in a car engine bay," Ms Strapp said.
"The animal (pictured) endured a night of pain and exposure to the elements and predators.
"Possums do not routinely sit on the ground, and it is always a sign that the animal may be in distress.
"The wounds have been dressed and the possum has pain management and antibiotics and has been placed with a FAWNA carer."
The Mail reached out to the department about the incident and the spokesperson said Parks and Wildlife Service staff were regularly involved in wildlife responses including responding to sick, injured or distressed wildlife.
"This can involve staff attending an incident and providing assistance on site, taking the animal to a vet (which may then be transferred to a rehabilitator) or occasionally caring for an individual animal for up to 12 hours until it is ready to be released into the wild again," they said.
Ms Strapp said the volunteers still needed help on the ground immediately.
"We certainly don't have time to wait around for grants to help us," she said.
"We just could not cope with another summer like that, we are exhausted, traumatised, and demoralised. DBCA has failed us and our precious wildlife."
The department spokesperson said anyone who finds injured wildlife should call the Wildcare Helpline on (08) 9474 9055.
"The Wildcare Helpline can offer advice on sick, injured or displaced native wildlife and refer callers to a wider network of experts for assistance," they said.