KNWVIKING...
Just a clarification of water bodies
SSL (seven seas lagoon) is the body of water in front of the magic kingdom. The TTC, POLY, and GF are on the shores and the monorail goes around it.
Bay Lake is where WL and FW are located. Discovery Island is in the middle of it. The CR is also on a shore of Bay lake.
SSL and Bay Lake are connected by a water bridge.
The EPCOT lake is World Showcase Lagoon
The lake between EPCOT and MGM which sits between BW and YC/BC is Crescent Lake.
Now for the tricky question: What is the name of the lake by Downtown Disney? This is the lake where you would take water mice if you rented them from OKW. Hmmmmmm.
Halle...
The plan is only good at the resort where you sign up for it. But the resort you sign up for the plan does NOT have to be the resort where you are staying.
SO....
If you stay at OKW, you CAN sign up at WL and use watermice on Bay Lake. But then you can not use the plan at OKW. If you sign up at OKW, you can not use the plan at WL.