A teenager reportedly seen hitching a ride on the back of a whale off the West Australian coast was courting death, say environmental authorities.



The WA Department of Environment and Conservation (DEC) was alerted on Friday afternoon that a teenager had been seen climbing onto the back of a southern right whale close to Albany's Middleton Beach, about 390km southeast of Perth.



DEC Albany district manager Mike Shephard said the report was being investigated, adding that even approaching a whale was crazy and illegal.



"Adult southern right whales can reach 18 metres in length and weigh up to 80 tonnes," he said in a statement on Sunday.



"If you are in the way of a tail slap or when it breaches, you are unlikely to survive."



Mr Shephard said boats must observe a 100m exclusion zone around whales while swimmers, surfers and kayakers must remain at least 30m away.



"This is to protect whales from being harassed or injured by boat strike and to protect people from harm," he said.



Harassing wildlife is an offence under Australia's Wildlife Conservation Act, carrying a maximum fine of A$10,000.