SOUTH PADRE ISLAND – Cameron County beach officials said although the water may appear calm on the surface, it's the dips on the ocean floor that can many times put people in danger.

A San Juan man drowned Tuesday on South Padre Island while trying to save his son struggling in the water.

Cameron County Beach Patrol Chief Art Hurtado said there was a moderate risk flag warning when the incident happened.

A yellow flag warning at the entrance of Andy Bowie Park or Cameron County Beach Access #2 indicates a moderate risk for swimmers.

"It means the waves have picked-up a little bit, but they aren't quite as dangerous yet," Hurtado said.

He said the yellow flags are used to alert beach goers that the waves are just about one to two-feet high.

Still, the water proved deadly Tuesday for the San Juan man.

Cameron County Chief Park Ranger Horacio Zamora said the 47-year-old was declared dead about an hour after he was pulled from the water. His son survived the incident.

He added neither knew how to swim.

It's unknown right now why the teen ventured out or why he got in trouble.

Hurtado said one common problem at county beaches is that often inexperienced swimmers rely on sandbars to keep walking out further into the ocean.

"The water comes in right where the sandbar is, so that's the peak of the sandbar," Hurtado said. "The water comes in and pushes right over that sandbar, that creates the wave. So, if you see a breaking wave, that's basically the peak of the sandbar."

"Unfortunately, right behind the peak is where the water suddenly gets deeper and drops down. So, people like playing in the waves, but if they step too far, that's where they get in trouble," he explained. 

Seattle native Kathy Atwood quickly noticed the change when she got in the water.

"I'm not feeling a lot of undertow, but it seems as there's different levels of the sand,. And that could be deceiving, where you might think it's shallow and it changes," she said. 

Atwood said she's visited beaches all around the world, so she's more cautious in unchartered waters.

"I just try to remember how Mother Nature can change at any moment, and can be unpredictable," Atwood said.

Hurtado said this is the first drowning in a guarded county beach this year. He added that there have also been 52 rescues.

The only county beach with lifeguards atop a stand is Isla Blanca Park.

Other county beaches, with the exception of Boca Chica Beach and Beach Access 6, have patrols driving up and down the beach. They will remain on patrol until Labor Day.