In its second year, an event celebrating boatmen and their boats. Originally for Venetian gondolieri, it is now open to most boatment and their boats, and most particularly to steamboaters. Although the closing date to register for special perks with a steamboat is April 15, I'm sure the organizers will give some leeway.
Even if you won't have a steamboat available, if you're going to be in east Europe check out the website at http://www.navalis.cz/en/st.-johns-river-festivites-navalis/
and see if it's something you'd like to see.