Bubbles on the surface
In several episodes Mike is on a boat trying to locate a diver's position by looking for bubbles that have reached the surface. Having been a certified diver who received his training in southern California where Sea Hunt was shot -- including ocean dives from a boat, I find it hard to believe that one can spot bubbles reaching the surface, with or without the use of binoculars, unless they're within a stone's throw of the boat. The ocean surface usually is too agitated by swells and waves to make out bubbles; furthermore, the surface returns to its previous state almost immediately after the bubbles surface.
I saw an episode tonight where someone is trying to spot a diver's bubbles from a seaplane with binoculars. That is even more unbelievable considering the distance a plane is from ocean and how hard it would be to spot a small area while passing by at the speed a plane has to maintain.