Hydro and Bubbles were introduced in the early 90’s as part of an advertising and marketing campaign. Hydro represented speed and intensity while Bubbles was all about fun and happiness. They used to give out stickers, key chains and other promotional items in the waterparks.
They didn’t really match the theme or focus of the waterparks, however. There was no solid link that justified keeping them around so they were phased out by 1997.