The Water/Shipwreck Gem is obtained when you complete all the quests in Shipwreck Shore.
"A sapphire given to you for passing Eve's trials and defeating the monster Old One. This is one of the Warden Keystones used to gain access to the Academy."
There is a world, Riverdeep, named after the Water Gem. The Riverdeep icon is the old look of the water gem