Detective Sergeant Simon Gray from Cumbria Police took on the Mid-Winter BoB Graham Round alone on Monday.
The idea to take on the physical endurance challenge came soon after Simon finished the Frog Graham Round back in August.
The route, based on the famous Bob Graham Round, starts and finishes at the Moot Hall, Keswick, but unlike the Bob Graham 24 hours club, there is no time limit to finish it.
It comprises of 40-miles of fell running, 16,000ft of climbing, and is split up with four lake swims.
Those who take part have to swim across Bassenthwaite, Crummock Water, Buttermere and Derwentwater, via all of the islands on the lakes.
The 31-year-old, who is the fourth person to complete the winter event since December 1 - and the first to finish the mid-water one - finished in a new record time of 11 hours and 49 minutes.
Simon said: “I completed the round alone, but had supporters helping me with food, drink, my wetsuit and supporting my kayak.”
“It is a spoof of the Bob Graham, but is actually a really decent challenge and takes you on a lovely route out towards the western fells.”
To classify as a mid-winter round, the contender has to complete the round between the weekend before the shortest day of the year and no later than January 10.
He added: “The Frog Graham Round actually caught my attention in 2013, I was told by my Dad about this book ‘Swimhiking in the Lake District’ by a chap called Peter Haynes.”
“He concocted this round along with other routes and gave instruction of how to make a ‘swim sac’ - this was effectively a rucksack with some armbands stuck down the side pockets, turned upside down and strapped to your back. Things have changed a lot with most people now using specially designed swim floats/dry bags to complete the Frog Graham.”
“In 2013, the Frog Graham Club didn’t exist and I didn’t know about anyone who had repeated Peter Hayes’ route.”
“Then, in August 2013 my now wife and I, who were just friends at the time completed the route of the round over two days as a fun, unusual challenge.”
“We had a great time and I always thought I would return to complete it over a day.”
Originally planned for December 18, Simon brought forward the event by a day due to the weather.
“Weather watching had been excruciating.”
“I decided to bring the attempt forward by 24 hours as there looked to be a weather window on the 17th.”
“The downside of this was that I’d just worked seven days straight before having to get up at 3.30am for an attempt, not the best prep.”
“The winds were also forecast to get up to 50-80mph after dusk so it was either a quick round or no round.”
The marathon was completed in four ambitious legs, Moot Hall to Beck Wythop, Beck Wythop to Crummock Water, Crummock Water to Horse Close, and finally, Buttermere to Keswick Moot Hall.
The day was documented by Jake McKenna, a young film maker from south of the county. He will make a short film of Simon’s challenge to be released online for free in January.
The Frog Graham Round can be done at anytime of the year, but verification must be provided to the secretary in order to be ratified.