You guys are getting confused, so here goes:
I HIGHLY doubt you can return to 'raft' the Lete River. If you are seeking the Water Dance, here it this (remember to bring Mog):

1) You can land your airship in two places, but I only remember one and that is the entrance to the cave with a waterfall right after the Phantom Forest.

2) Go down the waterfall and you'll end up in the Veltz.

3) Make your way to the cresent cave.

4) Swim the Serpent River

5) Get Mog's Dance: Water Rondo.

6) End up in Nikeah I think... (sh3t, memory is failing me )

7) Chocobo your way back to airship

8) and walah! Your Water dance.

And yeah, there are better ways to get the dances. There is only one dance you can't get yet and that is the Snow one. Water Rondo is pretty good.