Six people are attempting to set a new world record by swimming 12 lengths of Windermere.
Each swimmer will cover an average of two lengths of Windermere, under Channel swimming / BLDSA rules, which does not allow wet suits to be worn.
The current record for the longest fresh water relay swim is 124 miles (200km), set in Lake Powel, USA, in 2010.
The team, who set off on Friday, hope to set a record of 125 miles (201.6km).
They hope to finish towards the end of Monday.
Members of the team will take turns every hour to swim, with each of them swimming the equivalent of 21 miles (33.7 km).
Open water swimmer Thomas Noblett, 48, from Windermere, is one of those taking part.
Ahead of taking to the water Mr Noblett said: "With all of the weather fronts coming through, the lake is like the North Sea".
According to the team, the water temperature in England's largest lake is about 10C.
The other swimmers include Liane Llewellyn, 29, from Bradford; Keith Bartolo, 35, from Malta; Michelle Lefton, 24, from Windermere; Michelle Sharples, 41, from Manchester and Dee Llewellyn, 33, from Bradford.