There seems to be a bit of confusion as to what activates it this time around. Does anyone know for sure if it reverts back the the RSE effect, where you have to be below the surface through Dive, or if it retains the DPPt effect? And could someone provide some proof from the code itself, just for confirmation?
Just for reference:
The actual description: A somewhat different Poké Ball that works especially well on Pokémon that live underwater.
Bulbapedia lists it as having the RSE effect: http://bulbapedia.bulbagarden.net/wiki/Pok%C3%A9_Ball#Introduced_in_Generation_III
While Serebii claims the other effect applies or all games after RSE: http://www.serebii.net/itemdex/diveball.shtml
Only thing is I can't really say how often each of these pages are updated.