A canoeist has died during the annual Devizes to Westminster Canoe Race.
Race directors said they were "saddened" to report a person had died in the final stages of the race on Monday.
In a statement they added: "We are co-operating with the relevant authorities in investigating the incident fully."
The race is held every Easter over a course of 125 miles (201 km) from Devizes in Wiltshire to Westminster in central London.
The race directors said their "thoughts and condolences are with the family and friends of the paddler".
David Joy, chief executive of British Canoeing, added: "I'm sure our whole community will be deeply upset to hear the tragic news this morning that a paddler has lost their life whilst competing in the Devizes to Westminster Canoe Race."
The race is considered to be one of the world's toughest endurance challenges.
The first 52 miles are along the Kennet and Avon Canal and the next 55 miles are on the River Thames.
Canoeists pass through 77 locks and the race ends at Westminster Bridge near the Houses of Parliament.