Four Lincolnshire Police officers signed up to swim the equivalent distance to the length of the English Channel for charity on December 9.
PCs Nicola Hill and Rob McCracken and sergeants Sarah McNair and Dominique Salsbury will take turns to swim 1,408 lengths of the pool at the David Lloyd Health and Fitness Centre in Burton Waters, Lincoln.
The swim will start at 7am until about 9pm and each officer will take turns to swim in relay, and there will be one or two people in the water at a time.
The charities the officers are raising money for are the Lincolnshire Air Ambulance and an orphanage in Swaziland that has been set up by a retired officer.
“We’ve all been training hard for the swim, which will cover about 35 km (21 miles) in total,” said PC Nicola Hill.
“It will be a gruelling physical challenge, but we’re all spurred on by the causes we’re raising money for. Please show your support by sponsoring us.”
Chief Constable Richard Crompton said “Both of these charities are fantastic causes.
“People living in Lincolnshire hear on a weekly basis how the Lincolnshire and Nottinghamshire Air Ambulance saves lives.
“It is a vital service, which is almost totally reliant on donations from charity events like this. Some of the money is also going to an orphanage in Swaziland.
“This was founded by former Lincolnshire Police officer, Robin Stanton. He and his wife now devote their time, money and efforts to running it and helping the many disadvantaged children every year.
“It’s great to see our officers contributing to local and overseas causes and I wish them all the best in their efforts,” Crompton added.