Aqua Sacs are believed to be relatives of the Sap Sac, with blue rather than orange coloration, that have adapted to life underwater. When damaged, an Aqua Sac bursts, discouraging species from predating on it. Unlike a Sap Sac's chemical explosion, however, this mechanism is harmless to Samus, possibly due to the water-bound nature of the plants' explosions.
- "Will burst when subjected to impact or trauma. Believed to be in the same family as the Sap Sac, this plant has similar features. It will burst when exposed to force. This protective response keeps most creatures from feeding on it." — Logbook "Aqua Sac" (Metroid Prime)