The musician, real name Theophilus Tagoe, had been on vacation with a group of pals, including his girlfriend Janet Bandu and Ghanaian soccer ace Asamoah Gyan, near the coastal town of Ada.
They hired jet skis from the local Aqua Safari Resort on Saturday (05Jul14), but tragedy struck after Bandu fell off the back of Castro's water vehicle. The rapper jumped into the water to rescue her, but neither of them resurfaced.
Police have yet to recover Castro or Bandu's bodies, but tributes for the musician have already started to roll in on Twitter.com.
Lethal Bizzle writes, "My favourite Ghanaian artist #RIPCastro", while Tinchy Styder adds, "My thoughts go out to Castro, his friends & family! Words can't even explain the shock I got when I heard the news! You're with the angels!"