There are watercraft all over WDW, and many trips can be made by water instead of bus or monorail.
The largest watercraft are the three Magic Kingdom ferryboats, which take Guests from TTC to MK and back again. And they're actually a little fasster than the monorails.
Aside from the ferryboats, there is a fleet of several sizes of water taxis which make trips around the Seven Seas Lagoon and Bay Lake, from MK to the various resorts, and in a few cases, from resort to resort (
WL to FW to MK, Not true under current boat routing and WL to Contemporary). Some of these craft are large enough to accomodate
ECVs and wheelchairs, but some of the smaller ones are not.
There is also a large fleet of Friendship Launches which operate on the Epcot area waterways. Friendship launches run from International Gateway at Epcot, to all of the Epcot resorts, and to DHS. During some times of the year, the launches run all the way from Epcot to DHS and back in a single loop, and at other times, there arre two overlapping loops; I don't remember the exact order, but I think they are Epcot to YBC to Boardwalk, and DHS to Swan/Dolphin to Boardwalk. To get from Epcot to DHS you'd transfer at Boardwalk. These launches do NOT enter either park.
Inside Epcot, there is also a small fleet of the same Friendship Launches which operates entirely within the World Showcase Lagoon, taking Guests from Showcase Plaza to docks in Morocco and Germany. These launches do NOT leave the park. However, since they are the same model of boat as those which operate in the Epcot Resorts area, some folks get confused and think that the launches make pickups and dropoffs bot inside and outside the park.
Then there is a small fleet of water taxis which operate in the Downtown Disney area, making stops at two or three dock along the DTD waterfront and at Saratoga Springs, and up the Sasogoula River to both Port Orleans resorts.
I'm probably forgetting some watercraft, but those are the ones I use when I'm at WDW. I highly recommend all of them, not simply as transportation, but as attractions in and of themselves. Nothing beats the views from the MK ferryboats on approach to the park in the morning, or the views from the Friendship Launches in either World Showcase Lagoon or Crescent Lake. Day or night, these craft are well worth your time and attention.
