I got a kick out of this discussion cause I've also giggled at the pictures of the "swimming" at the lagoon - the lovely female model sitting with her feet in the lagoon while the Pool CM delivers her Pina Colada out from the beach.....yeah right!
It was my impression as well that the Seven Seas Lagoon, while having a wonderful name, is only a large man-made collection pond filled with regulated incoming and outgoing waters from the groundwater swamps that surround WDW. A few years back I went on one of the old Disney Institute canoeing programs which went on one of the irrigation canals out back behind the Magic Kingdom. If I recall correctly, as we paddled through the dark brown water teeming with little gators, we were told that the Disney water engineers have, since WDW was created, engineered this amazing (but sometimes criticized by environmental groups) water control system that feeds or drains all of those natural looking waterways, ponds and lakes that make up WDW's aqua design.
And I believe THAT is what feeds the Lagoon. And since it's filled with all of the wild and wonderful bacteria and algae and and thousands of water inhabitants that grow and prosper in the warm Florida weather, I'm not sure I would want to swim in it.
And if a gazillion little amoebas aren't enough to keep me out of the water, I think the occasional gator that slips through the control dams and gates that surround the water area are enough to have ME doing my belly flops in the new Grand Floridian pool and not in the picturesque waters of the Seven Seas Lagoon.
Dave in the Frozen North
(Who lives in very simlar swamp land (called muskeg) that differs from the Florida Swamp only by the fact that it's frozen 8 months of the year. Oh yeah, and we also deduct the Gators and add the beavers!!)