Aquazone / Hydronauts Minifigs

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.

Aquazone was an underwater theme introduced by LEGO in 1995 that lasted until 1999 and contained five subthemes all of which took place in the ocean and typically involved two sides fighting each other for valuables such as Hydrolator Crystals.