SHARKS HAVE BEEN CAST AS THE ULTIMATE VILLAIN EVER SINCE THE MOVIE "JAWS."

IT WAS RELEASED 50 YEARS AGO THIS SUMMER, TELLING THE STORY OF A MAN EATING GREAT WHITE SHARK TERRORIZING BEACHGOERS.

BUT THE REALITY IS HUMANS ARE A BIGGER THREAT TO SHARKS THAN THE OTHER WAY AROUND.

AN ENDURANCE SWIMMER WANTS TO GET THAT MESSAGE OUT BY SWIMMING AROUND MARTHA OR -- MARTHA'S VINEYARD TO GET THE MESSAGE OUT.

HERE AGAIN IS ALI ROGIN.

ALI: ENDURANCE SWIMMER LEWIS PUGH IS SWIMMING 60 MILES AROUND MARTHA'S VINEYARD.

LEWIS: I SWIM FOR AS FAR AS I CAN EACH DAY.

WE THEN MARK THE POSITION ON THE MAP.

I GO AND SLEEP AND THEN I GET BACK IN THE NEXT DAY AT EXACTLY THE SAME SPOT AND CARRY ON.

ALI: IN JUST A SPEEDO AND SWIM CAP, PUGH FACES WIND, ROUGH WATERS, AND, MOST UNPREDICTABLE OF ALL, SHARKS IN THE DEPTHS BELOW.

BUT THE SHARKS ARE THE POINT.

LEWIS: FOR THE PAST 50 YEARS IT'S ALL BEEN ABOUT FEAR AND ABOUT THE DANGER OF SHARKS.

WHAT I WANT TO DO IS I WANT TRY TO CHANGE THE NARRATIVE FOR A NEW GENERATION AND SAY, SHARKS ACTUALLY BRING LIFE, THEY SUSTAIN LIFE, THEY MAKE OCEANS HEALTHY.

ALI: AND HE SAYS THERE'S NO BETTER BACKDROP FOR THIS MESSAGE THAN THE PLACE WHERE THE "JAWS EFFECT" WAS BORN.

LEWIS: IT PORTRAYED SHARKS IN A WAY THAT THEY ARE VILLAINS, THEY'RE OUT TO GET HUMANS, AND WE KNOW THAT THEY'RE NOTHING OF THE SORT.

AND SO THIS IS AN OPPORTUNITY TO TRY AND TELL A NEW NARRATIVE FOR A NEW GENERATION.

ALI: GLOBALLY, ON AVERAGE, 274,000 SHARKS ARE KILLED EVERY DAY.

THAT'S A HUNDRED MILLION SHARKS A YEAR.

LEWIS: IT'S AN ECOCIDE WHICH IS TAKING PLACE RIGHT NOW.

IT'S COMPLETELY UNSUSTAINABLE.

IT'S ABSOLUTE MADNESS.

AND IT'S GONNA LEAD TO A WATERY DESERTS.

ALI: THE GREATEST THREAT IS FROM OVERFISHING, BUT IT'S EXACERBATED BY STIGMA.

LEWIS: SHARKS ARE ABSOLUTELY AMAZING ANIMALS.

I MEAN, THEY'VE BEEN AROUND SINCE BEFORE THE DINOSAUR.

THINK ABOUT THAT.

THEY'VE SURVIVED FIVE MASS EXTINCTIONS, AND YET THEY ARE REALLY UNDER THREAT RIGHT NOW IN OUR GENERATION.

WE'RE THE ONLY GENERATION THAT CAN NOW SAVE THE SHARK FROM EXTINCTION.

ALI: THIS SWIM IS MEANT TO CELEBRATE SHARKS, BUT PUGH IS STILL ENCROACHING ON THEIR HOUSE.

HE IS ACCOMPANIED BY A KAYAKER WHOSE VESSEL HAS A SHARK SHIELD, AN ELECTROMAGNETIC DEVICE THAT DETERS SHARKS WITHOUT HARMING THEM.

LEWIS: SO I'M TALKING SHARKS SHARKS SHARKS.

I THEN NOW GOT TO GET INTO THE WATER AND START DOING THE SWIM.

WELL YOU CAN IMAGINE WHAT I'M THINKING ABOUT, RIGHT?

AND SO EVERYTHING, EVERY LITTLE SHADOW WHICH YOU SEE PERHAPS IS A ROCK UNDERWATER, EVERYTHING SORT OF KIND OF LOOKS LIKE A SHARK.

AND SO IT'S SO IMPORTANT THAT I JUST KEEP MY MIND CALM AND JUSUS SAY, LEWIS, JUST KEEP CALM, CARRY ON.

IT'S VERY, VERY EASY FOR THE MIND TO GET CARRIED AWAY IN THE WATERS OF CAPE COD.

ALI: PUGH IS NO STRANGER TO TOUGH CONDITIONS.

HE REPRESENTS THE UNITED NATIONS AS PATRON OF THE OCEANS, AND WAS THE FIRST PERSON TO COMPLETE A LONG-DISTANCE SWIM IN EVERY OCEAN OF THE WORLD.

HE CROSSED THE NORTH POLE.

DOVE INTO THE ICY WATER IN ANTARCTICA.

SWAM THE LENGTH OF THE HUDSON RIVER.

AND THROUGH THE CORAL REEFS AND SHIPPING CORRIDORS OF THE RED SEA.

ALL TO RAISE AWARENESS ABOUT THREATS TO OUR OCEANS.

BUT THIS SWIM, HE SAYS, IS ONE OF THE MOST CHALLENGING OF HIS CAREER.

IT'S LONG, IT'S COLD, AND IT'S MENTALLY GRUELING.

THE MORNING WE SPOKE TO HIM, HE MANAGED TO GET IN TWO OF HIS PLANNED 10 KILOMETERS FOR THE DAY IN A BRUTAL PRE-DAWN SWIM.

LEWIS: SO THERE I FIND MYSELF LOWERING MYSELF SLOWLY INTO THIS DARK, DARK BLACK WATER.

AND THE COLD, IT JUST GNAWS ITS WAY INTO YOU, DAY AFTER DAY AFTER DAY.

THIS TYPE OF COLD WHICH DEMANDS AN ANSWER.

WHY ARE YOU IN HERE?

ALI: ON THIS SWIM, HE'S IN HERE FOR THE SHARKS.

FOR PBS "NEWS WEEKEND," I'M ALI ROGIN.

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