Bayside Council has received a report of a large venomous blue-ringed octopus sighting in the water off the beach at Dolls Point.
The sighting was reported on Monday in the lagoon area.
The octopus is tiny and turns bright blue when threatened.
Bayside Council issued a double warning following the sighting.
"Please be careful. Do not try to kill it as all native animals are protected. Do not touch it if you see it and stay well away as it is highly venomous," the council posted on its Facebook site.
"The blue-ringed octopus found in the rock pools around Botany Bay may look small and harmless, but it is actually small and deadly.
"Its colourful appearance makes it very tempting to touch or hold, but please don't.
"Other local native fauna to look out for that can sting include sting rays and bluebottle jellyfish. And you might feel sea lice (jellyfish larva).
"The best advice for adults and children alike is, look but don't touch.
"And do not try to kill it as all native animals are protected."
In May 2019, a blue ringed octopus was sighted on the beach by a man walkiing with his young daughter at Dolls Point and another at Ramsgate Beach.
And in the same year a young girl unknowingly picked up a shell with a blue-ringed octopus hiding inside at Salmon Haul Reserve, Cronulla.