I would think the water there was green not because it was unhealthy (public wouldn't be allowed to be in it if so) but for a similar reason to why the water in the Jungle Cruise & Rivers of America is green. In River Country's case, I would think it's just a themeing thing since it's supposed to be 'an old-fashioned swimming hole'. The contrast though its unfavorably noticeable to the clear water in other water parks.
-- PMM