Nolan Wells' family may not be convinced he drowned off the coast of Horn Island ... but some of the area locals say they wouldn't be surprised -- because the waters have claimed other lives.

Here's the deal ... NBC News spoke to several people who regularly visit the area -- all anonymously due to the media scrutiny around the mysterious case -- including a boat operator who gave a rundown on the area's current.

The boat operator said, "I know people that have grown up out there that have died out there. It’ll humble you very quick. I don’t care what kind of shape you’re in. Those currents can get you, and before you even realize you’re in trouble, you’re gone.”

Of course, Ben Crump -- the attorney for the Wells family -- has argued that it's unlikely Nolan drowned because he knew how to swim ... which the boat operator here is basically saying doesn't guarantee anything.

NBC News also talked to people who explained the culture around a Horn Island weekend ... including how vacationers often meet up with other groups and catch rides back with other friends.

This would help explain Nolan choosing to stay behind at Horn Island at 3 PM on July 4 instead of heading back with his original group of pals, as they claim. They also had his phone ... which some told NBC News is normal because it's a safe, dry place to keep it while you wade about in the water.

As you know ... Nolan was found dead on July 6 ... and authorities have said they believe he drowned, though they're continuing to investigate.

Crump and the Wells family have pushed for their investigation ... voicing that they do not trust Mississippi authorities due to the history of the Deep South.