Ted Simpson, 22, from Manchester, and James Reilly, also 22, from Guernsey, paddled down the loch in four hours 43 minutes and 43 seconds.
This week they kayaked 74 miles (120km) of the River Spey from Kingussie to Spey Bay.
They covered the distance in 15 hours, 51 minutes and 43 seconds.
The pair said it was a new fastest time for the journey, which took them from the Highlands to the Moray coast and raised money for the Cystic Fibrosis Trust.
To make sure they reached Spey Bay before it got too dark, they set off at 05:00.
Mr Simpson said: "We were completely spent by the end of the day, but really proud to have given it our all to raise awareness and funds for such an important cause."
The pair's time for the 23 mile (36km) crossing of Loch Ness last year beat a previous time of five hours and 19 minutes.
Two friends who set a new Guinness World Record for the fastest crossing of Loch Ness by tandem kayak last year have claimed a new achievement.