Rescue workers are continuing to search for a missing man who is believed to have got into difficulty in a stretch of water connected to the River Thames in Berkshire.
Officers from Thames Valley Police were called to an area at Lulle Brook, between Odney Lane and Mill Lane, Cookham, at around 7pm on Tuesday.
Police received reports that two men had been swimming in the water and got into difficulty.
The Royal Berkshire and Buckinghamshire Fire and Rescue Services, the South Central Ambulance Service and the Berkshire Lowland Search and Rescue, all also attended the scene.
Police said one man in his thirties was helped to safety by a member of the public and taken to hospital, where he remains in a serious condition.
The search is ongoing for the other missing man, also said to be in his thirties.
A third man who entered the water to help was left unharmed, police said.
Superintendent Colin Hudson, LPA Commander for Windsor and Maidenhead, said: “We are carrying out searches today to locate the missing man which includes searches on the banks of the river and in the water using specialist resources.
“One man remains in hospital in a serious condition.
“Our thoughts are with both the men’s families and our officers are supporting them at this very difficult time.”