In 1998 and 1999 which was the tail end of the Aquazone theme featured the Hydronauts, a story line that involved a battle between the Hydronaut miners and the fish-like Stingrays. The set's color scheme was similar the one of the Aquanaut sets but was different in that the transparent pieces which were now exclusively transparent green instead of blue and trans-neon orange. The Hydronauts minifigures had unique masks printed onto their faces which gave them a very alien look.
1998 LEGO Sets
1998 marked LEGO’s leap into programmable play with the launch of LEGO Mindstorms, combining motors, sensors, and code for user-built robots. LEGO also entered digital entertainment with games like LEGO Creator, LEGO Loco, and LEGO Chess. New themes included Adventurers, following Johnny Thunder’s global expeditions, and Insectoids, a sci-fi successor to Exploriens. LEGO Castle revisited classic factions such as Crusaders and Dragon Masters, reconnecting with its medieval roots while bridging into modern set design.