What body of water could this possible be??  And what hair product does Mark use to ensure that nary a lock is out of place, even after swimming underwater??

I am glad that the bubbles in panel one are being created by Mark exhaling, and not some giant school of fish collectively breaking wind…  Well, the adventure’s not over, kids, the other two (can’t bring myself to type their names…) have to find there way out without dying and Mark has to find his way to shore… that should only take another month or two…