A “Pig & Run” half-marathon in Brittany where the winner is awarded his or her bodyweight in pork has sparked a backlash with thousands calling for a boycott on grounds it is unethical and bad for the environment.

While it is popular with runners – the race is already full – the event has appalled animal rights activists, vegans and, above all, environmentalists who blame intensive pig farming in Brittany on the rise of potentially deadly toxic green algae washing up on its shores.

On May 18, some 500 competitors will set off on a 23.5km race along roads and paths around the famed Ria d’Étel, a maritime gulf fed by several rivers of southern Brittany.

However, there is a twist to the trail as participants will set out from a pig farm and rather than taking energy bars at pit stops will be offered barbecued pork sausages, scratchings and other “cochonnailles” (pig-related products) along the way.

As Le Parisien put it, “not all the loins on show will be those of the runners”.

To crown it all, the winner will take home his or her weight in pork.