The Wave Shaft is one of the two parts needed to create the halberd called Wave. The other part is the Wave Blade. This item appears in Baldur's Gate II: Shadows of Amn and Baldur's Gate II: Enhanced Edition.
This part can be found in the Planar Prison during the companion quest Rescue Raelis and Haer'Dalis from the planar prison.
|“|| Part of the Wave
This is a piece of the Wave, a powerful halberd created as a weapon of vengeance by a cult worshipping Umberlee. It apparently draws water out of its victims, and is able to slay creatures of fire almost instantly. Tales say the Wave was lost long ago to the fire giants of the Storm Horn Mountains, but was eventually found by the adventurer Arganon of the Long Reach. He either lost the weapon to a wager in the planar city of Sigil, or it rests with his bones when his ship was sunk during a great storm in the Sea of Swords. No one knows for sure.