It gets better. In order to ensure that nobody accidentally floated up to the surface, the actors were all strapped down with weights, meaning weak swimmers were screwed, and strong swimmers ... were also screwed. Yes, Cameron kept his actors in line with the same method the mafia uses to dispose of bodies.
All the hard work and stress (along with the constant threat of decompression sickness) caused Harris to break down and cry one evening and Mary Elizabeth Mastrantonio to famously scream "We're not animals here!" before storming off the set. Cameron responded to their extremely understandable concerns by calling anyone who couldn't keep up "wussies," because this was before he filmed Titanic and invented the concept of love.
Mark Thiessen/National Geographic
Love of water, and of hypothermia. Which wouldn't really have helped matters.
In fairness to Cameron, he was putting his life on the line right there with them. One day both Cameron and his assistant forgot to check the oxygen meter on his tank and, well, you can guess what happened next. Again, a safety diver gave him water instead of air, and Cameron had to cold-cock him in the face so he could escape to the surface moments before blacking out. Both the diver and the assistant were fired, and humanity narrowly avoided living in a dark timeline where Terminator 2 was never made. If you can call that living.