Sacha Dench, who was attempting a world-first circumnavigation of mainland Britain to raise awareness about climate change, has been seriously injured after a paramotor accident in the western Highlands of Scotland.
Dan Burton, a member of her support staff, was killed during the incident.
Ms Dench had been dubbed the "human swan" as she attempted a 3,000-mile Round Britain Climate Challenge ahead of the Cop26 conference due to start on October 31.
In statement, the trustees of the Conservation Without Borders, which was founded by Ms Dench, said the accident happened near Loch Na Gainmhich in the far north of Scotland.
The statement said: "We are very sorry to have to confirm that Dan Burton, the support paramotorist has died as a result of the accident.
"Sacha Dench is seriously injured and is being treated in hospital. Her injuries are serious but not life-threatening
"Both highly experienced paramotorists, our thoughts are with the family of Dan Burton to whom we offer our sincere condolences.
"The incident was attended by police and medics and enquiries are underway to establish the details of the accident."
The statement added that the families of those involved had been informed and that the Round Britain Climate Challenge would now be put on hold.