I think it closed due to a health and safety issue - the water hole water could not be kept clean enough as it was not man made I dont think there is anything there now
I think the buildings are still there. They didn't replace it because the visitor numbers can't sustain three water parks. With Aquatica due to open I think it's even less likely now.
I'm not sure how true this is, but aparently the water used at river country came directly from the seven seas lagoon and it became too hard/costly to keep clean as the water in the seven seas became more dirty.
I think also there was an element of laziness and can't-be-bothered-ness (grumblegrumblethanksalotIsnergrumblegrumble). It cost too much to keep it running, wasn't making enough money so it was bye bye swimming hole . There's nothing new there, they've just left it to go to waste. If you do a search on these boards for River Country, you'll probably find a few of them have links to Google Earth pictures of it. It's not looking too happy.
Anywhom.... If you get yourself a rental boat and head out towards Discovery Island (I think its called that) Its right near there. Its in a sorry old state! Check out virtual Globetrotting.... You can get a birds eye view of it