Most swimmers will be take to the waters of Windermere to swim a mile (1.6Km) with some longer swims scheduled for Sunday.
The event is expected to attract 10,000 swimmers, organisers said.
A 10k marathon distance has also been introduced and is expected to take experienced swimmers four hours to complete.
Great Swim Director Alex Jackson said: "The Great North Swim is proving to be as popular as ever, with 10,000 expected in Windermere for our ninth event here."
Introducing the "10k event will provide a new challenge" he added.
Thousands of swimmers have headed to the Lake District this weekend to take part in the Great North Swim.