ACT Health is warning Canberrans not to pick and eat any wild mushrooms as death cap mushroom season begins.

There have been four deaths and 12 reported cases of poisoning in the ACT due to death cap mushrooms in the past 14 years.

Death caps are the world's deadliest mushroom and ACT Health Protection Service director John Woollard says they can easily be mistaken for edible mushrooms.

"We do live in an area where we get seasonal growth of death cap mushrooms and the message is for people just to take care and be aware of that risk in the environment.

"We recommend that people don't harvest wild mushrooms themselves, they get them from the store instead."

Death cap mushrooms grow mainly near established oak trees in autumn.

Key points: Most poisonous mushroom in the world

Most poisonous mushroom in the world One mushroom is enough to kill an adult

One mushroom is enough to kill an adult Four people died, 12 sick in ACT in 14 years

Four people died, 12 sick in ACT in 14 years Death caps look similar to edible mushrooms

Death caps look similar to edible mushrooms May be white but usually pale-green to yellow in colour

May be white but usually pale-green to yellow in colour Feature white gills and white or pale-green stalk

Feature white gills and white or pale-green stalk Mainly found in the ACT and parts of Victoria

Mainly found in the ACT and parts of Victoria Commonly found near established oak trees

Commonly found near established oak trees The entire mushroom is poisonous

The entire mushroom is poisonous Cooking or peeling does not remove toxicity

Cooking or peeling does not remove toxicity Symptoms occur six to 24 hours after eating

Symptoms occur six to 24 hours after eating Symptoms include abdominal pain, diarrhoea, vomiting, seizures

Symptoms include abdominal pain, diarrhoea, vomiting, seizures If consumed seek immediate medical attention

"It can be extremely difficult for even experienced collectors to distinguish the small button death cap from an edible mushroom," said acting chief health officer Dr Moira McKinnon.

"The fully-grown death cap mushroom cap is silky smooth, and its colour varies from white to greenish-brown.

"The gills are white, unlike the pink or brown gills of the common field mushroom. The stem is white to pale yellow-green."

The mushrooms contain a toxin that attacks the liver and can cause death through liver failure.

"Even a small piece of a single mushroom can be enough to do a lot of damage, it's a very poisonous substance," Mr Woollard said.

"Cooking has no effect on the toxin at all."

Mr Woollard says symptoms of poisoning can begin within six to 24 hours after eating them.

"Symptoms include violent stomach pains, nausea, vomiting and diarrhoea and if people have got any symptoms like that they're better to get checked out - rather be safe than sorry," he said.