Seventy-four-year-old Venetian Paolo Donaggio and his friend, 62-year-old Austrian Peter Rauscher, will begin the epic gondola journey on May 12th in Pavia, Nuova Venezia reported.
From there they will row down the River Po until they reach Venice, where they will hand-deliver the love letter.
The journey will comprise some 430km and the pair will travel around 80km per day, at a speed of about eight km per hour.
The pair have had a gondola specially restored for the occasion which has even been fitted with an Austrian flag.
The sender and recipient of the epistle are as yet unknown and the two are sworn to secrecy.
Rauscher first became fond of Venetian rowing two years ago, before purchasing his own gondola a year later.
Swimming champion Donaggio, who is nicknamed “croccodillo” (crocodile) in Italy, was in 1979 given the title of World Marathon Swimming Champion by the World Professional Marathon Swimming Federation.
Almost three decades later in 2006, the then 65-year-old swam from Chioggia and Venice, setting a new record.