Maybe you can run for a bit under water, stop and set a portal, then portal out. recover, portal back in, run, set another, portal out, ....Or go for a bit, then stop, reqeuip (swapping the scuba to the other 4), go , reequip.
Or just let 4 live, let the others drown, then resurrect on the other side (kind of the Abyss method).
Tools for Wizardry(r) 7