There was a documentary on Discovery HD Theater titled "People of the
Lake" with this description: "Along Lake Isnle, more than 80,000
people spend their lives in stilted villages above the water." There
is no mention of "Lake Isnle" in Google or anywhere else I can find.
Where is it and what is it actually called?

Hello.

I'd imagine that they meant "Lake Inle" which is in Myanmar (Burma)

See:

Lake Inle, Burma
http://perso.club-internet.fr/pchanez/Images3/landscape_10.html

Lake Inle scenery
http://www.molon.de/galleries/Myanmar/LakeInle/SceneryVillages/imagehtm/image9.htm

Travel Picture: Lake Inle
http://www.traveljournals.net/travelpictures_view.asp?pic=1722

Terra Galleria: Inle Lake
http://www.terragalleria.com/theravada/myanmar/inle/inle.html

PlanetWare: Myanmar Inle Lake
http://www.planetware.com/photos/MYA/MYA036.HTM

"Inle Lake is home to 70,000 Bamar, Danaw, Danu, Intha, Kayah, Pa-O,
Shan, and Taung-yo peoples, among others - roughly half of the areas
population.
Of these groups, one of the largest is the non-indigenous Intha, who
live in 17 stilted villages around the lake. They are said to have
migrated from Dawei, in southern Myanmar, in the late 1300s."
source: visit-mekong.com Inle Lake
http://www.visit-mekong.com/myanmar/jewels/Inle_lake.htm

search strategy:
"stilted villages", lake

I hope this helps