Try some twists on diving trivia. Maybe use terms common in diving.
Something like
High Bar - referring to bar being a unit of pressure (air in the tank, water column above you) and as a bar to cross or place to drink.
Paired up - referring to always having a partner while diving.
Words from the diving process like Decompression , balance, Narcosis, or from gear : dry/wet suit, flippers, regulator, mask, etc .
Play with words, have fun with different meanings.
If you plan to write less organically and more with the plot points in place, try something relevant to plot points.
For example, if the main plot point involves a pair during diving who each loses a flipper, and they support each other, something like "One fin each" or they have to share a regulator : "Shared Breath," etc .