Graham Donald and Kerran Traynor set off from Loch Linnhe on September 13 and made their way through rivers and lochs in the Great Glen area, passing through water the entire way.
The pair crossed 120km of open water, passing through Loch Lochy, Loch Oich, Loch Dochfour and Loch Ness, before finishing in the Beauly Firth at Inverness.
Graham and Kerran have raised just under £3,200 for Marie Curie and Gambia’s Bansang Hospital Appeal.
The pair said the feat had never been done before.
Kerran, 31, said: “Graham mentioned the idea over a pint in passing and then a month or so down the line I asked what’s the plan.
“It’s almost like someone’s drawn a line for us to swim along.”
Graham and Kerran had originally planned to complete in a run-swim-run event last year until Kerran ruptured his Achilles and had to have surgery in December.
Graham, 27, said: “It started out as a bit of an idea but then all of a sudden people started sponsoring us, and we thought now we really do have to do this. “We were spurred on by the people supporting us.
“We thought ‘Wow, this is actually happening’. It all went really smoothly and it was good to tackle.”
Graham chose to sponsor Marie Curie because his grandmother, Joyce, suffered from breast cancer in 2009, and his great-grandmother also suffered from cancer in the 1980s.
Kerran’s charity of choice, the Bansang Hospital Appeal, is run by the mother of a friend from university, Anita Smith MBE.
Kerran added: “She runs the whole charity and she does it pretty much single-handedly.
“She has endless amounts of generosity so wherever possible I try and get on board and help them out.”
The volunteer team was led by Graham’s father, John, and uncle, Tom, and were there throughout their challenge.
They gave themselves two weeks to complete the challenge but finished early after just 10 days.