Bubbleweed (3.5e Equipment)
From D&D Wiki
Bubbleweed is a type of seaweed that releases oxygen when chewed, allowing the user to effectively breathe underwater. It grows in some saltwater reefs, usually between 100 and 200 feet below sea level. The color of bubbleweed ranges from soft pink to deep purple. It is mostly harvested by specialized ships, but passing sailors have been known to collect it to be sold on a small scale.
Effect: A handful of bubbleweed can supply oxygen to a medium creature for 4+1d4 hours.
Cost: 5gp per handful.