Tourists are being warned to avoid rotting seaweed in France, which may have killed a young oyster farmer.

Environmental groups Safeguard Trégor and Stop Green Algae believe the abundant sea lettuce is to blame for the 18-year-old worker’s death in the Bay of Morlaix, in Brittany, on Saturday.

As it rots, seaweed gives off hydrogen sulphide (H2S) – a colourless and highly poisonous gas which smells of eggs.

Public prosecutors are said to have ordered a post-mortem examination to find out the cause of the teenager’s death, according to The Times.

Fears surrounding “killer seaweed” in France have been growing for a number of years.

Rotting seaweed blights Mexico beaches Show all 10 1 /10 Rotting seaweed blights Mexico beaches Rotting seaweed blights Mexico beaches Tourists spend a day at a beach covered in seaweed in Cancun, Mexico on June 24 Reuters Rotting seaweed blights Mexico beaches A worker cleans piles of sargassum, a seaweed-like algae from a beach in Tulum, Mexico on June 15 Getty Rotting seaweed blights Mexico beaches A worker cleans piles of sargassum, a seaweed-like algae from a beach in Tulum, Mexico on June 15 Getty Rotting seaweed blights Mexico beaches Tourists spend a day at a beach covered in seaweed in Cancun, Mexico on June 24 Reuters Rotting seaweed blights Mexico beaches Water off the coast of a resort in Tulum, Mexico are brown due to sargassum, a seaweed-like algae on June 15 Getty Rotting seaweed blights Mexico beaches Sargassum, a seaweed-like algae, lines the coast of a beach in Tulum, Mexico on June 15 Getty Rotting seaweed blights Mexico beaches A worker uses a Bobcat to clear seaweed from a beach in Cancun on June 15 Getty Rotting seaweed blights Mexico beaches A worker cleans piles of sargassum, a seaweed-like algae from a beach in Tulum, Mexico on June 15 Getty Rotting seaweed blights Mexico beaches Water off the coast of a resort in Tulum, Mexico are brown due to sargassum, a seaweed-like algae on June 15 Getty Rotting seaweed blights Mexico beaches Workers pile up seaweed after removing it from a beach in Cancun on June 15 Getty

Increasing amounts of the algae is believed to be linked to nitrate pollution caused by intensive farming.

Concerns were reignited in 2017 when a man out running collapsed and died near Saint-Brieuc.

His death was considered to be caused by a heart attack – but it was later pointed out that it was the same stretch of beach where 36 wild boar died in 2011.