“The citizens of Azeroth need a break. Let’s go to Thousand Needles!”
The Thousand Boat Bash, aka Boat Day, is an event in which adventurers go to Thousand Needles and enjoy a day at sea. Races from around the world come to Thousand Needles, this includes races of the Horde and the Alliance and Tuskarr.
If you open the map of the zone, you’ll see the world quest
Boat Tour available, near Fizzle and Pozzik’s Speedbarge. This is where you head to start things off of a series of quests to eventually create the final reward for this micro-holiday: 
Small Boat. A quick way to get to Thousand Needles is to use the Uldum portal in Stormwind/Orgrimmar and fly up from there.
Once you enter the area, a message will pop up letting you know you have a free boat for the day, which casts the spell Boat Day on you. Just land in the water, jump up and your boat will spawn, allowing to speed around the area. Or you could fly, but that’s missing out on the spirit of Boat Day!
Note: All the ships have rope ladders on the side that you can click to board them.