EDIT: Thanks to gingicat for identifying the movie as Breakthrough. As a reviewer, I dis-recommend it, EXCEPT for use in classes about medical ethics, writing/filming ethics, water/ice rescue or other first responder training, or other cases where its discussion value exceeds its damage quotient and can be presented with appropriate warnings beforehand.
1) About a third of drowning deaths are would-be rescuers, and some of these are ghastly La Brea tarpit incidents where attempts to save one person kill a whole bunch of others. Of course there's a human instinct to rescue those in danger, but in some circumstances it's the wrong thing to do. If you want to be heroic, learn water rescue and ice rescue; and if you haven't done those things, don't get involved in a water rescue attempt. The life you save may be your own.
2) This is where it gets really ugly. Modern medicine can save a lot of people it shouldn't. An analytical look at survivable submersion times shows that rescuers typically persist in searching long after the window of good outcomes. In almost all cases, brain death occurs between 4-6 minutes without oxygen, and significant damage can occur considerably sooner.
Several studies have demonstrated the relationship between submersion time and survival (5,6), including a case series of children that found the risk of death or severe neurological disability to be 10% for 0 to 5 minutes, 56% for 6 to 9 minutes, 88% for 10 to 25 minutes, and 100% for greater than 25 minutes.
The outcomes for adults are worse than those. Beyond the first few minutes, a lot of "rescued" drowning victims are then left with permanent impairments, some of which are extremely miserable -- not just for themselves, but for their families. Consider that quick death may be preferable to life where every breath hurts, or just existing in a damaged brain is confusing and awful because nothing works right anymore. It's a spectrum. Toward the short end, impairment may be minor and quite livable. But at the far end it's downright torture just to be alive.
When we tell stories, they stick in people's minds. That movie tells a story that people will want to believe -- the idea of heroic rescue saving a life. It will encourage them to keep looking, even in dangerous conditions, even when the prognosis after rescue is quite grim. It increases the likelihood of rescues after lengthy submersion. And that curve looks a lot like exposure to a zetetic hazard: most people get sick or die, while a few manifest superpowers. It's not a flashy one, but Super-Constitution is real and if someone walks away unharmed from a long drowning, there it is.
Will people watch that movie and think, "Hey, I should learn water safety and water rescue?" I doubt it. My parents' home is within view of a river that often kills people in winter. The nearest town to me has a dam with a big sign listing all the people who have died sliding down it. But people still walk over the river ice and slide down the dam. Darwin Awards, really.
This movie is not my idea of responsible storytelling. Sure, it's valid. It's attractive; it may well prove popular. But it's going to do more harm than good.
Tell all the stories. Just consider that some of them might be best kept in a drawer.