In 1990, as part of a ride rotation program, a stand up looping roller coaster called Shockwave was added to the park. Shockwave had previously operated at Six Flags Magic Mountain. However, Ultra Twister was removed at the end of 1989 and sent to Six Flags Astroworld for the 1991 season keeping the park's coaster count at five. In 1991, the park added a huge complex of "dry" waterslides. While guests got wet on them, they could ride these with regular clothes or swimsuits. These slides were themed after the rivers of the world. Roaring Rapids, as well as the second flume ride in the park, were incorporated into this complex. Roaring Rapids became Congo Rapids, and The Hydro Flume became Irrawaddy Riptide.