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.
1999 LEGO Sets
1999 was a landmark year with the launch of LEGO Star Wars, the company’s first licensed theme, debuting alongside The Phantom Menace. This partnership with Lucasfilm transformed LEGO’s strategy and ushered in the era of licensed themes. New original lines included Rock Raiders, Slizers (Throwbots), and Adventurers: Jungle, while LEGO Education was formally established from LEGO Dacta. Several older themes—Cyberslam, TechPlay, UFO, Insectoids, Znap, and Model Team—were retired, marking a clear generational shift toward modern play concepts and digital engagement.