When Richard Ladkani said yes to filming Sea of Shadows with Academy Award-winner Leonardo DiCaprio, exposing how Mexican drug cartels and Chinese traffickers are bringing the rare vaquita porpoise to the brink of extinction, he had no idea it would turn deadly.

Not only did Ladkani and his team get caught up in a riot in Mexico — with bullets flying past and stones being hurled their way — they later became the target of the powerful cartel that was less than pleased with their efforts to expose their illegal exploits. And they were stunned when one of the people they interviewed anonymously in the film ended up murdered.

“People have no idea any of this is happening,” Ladkani tells PEOPLE.

As dangerous as it is, the award-winning Australian director-cinematographer says it’s a story that’s too important not to tell.

“The war is on,” Ladkani says. “We’re losing, but maybe this movie can turn things around. That’s why we are so passionate about this."

He adds, “People need to see the movie and they need to get angry and rise up and spread the word that this has to end."

Leo DiCaprio’s Nat Geo Thriller Exposes How Quest for 'Cocaine of the Sea' Kills Rare Vaquita_1
Leonardo DiCaprio, Jane Goodall, and Richard Ladkani at National Geographic Documentary Films’ Sea of Shadows Los Angeles Premiere on July 12, 2019Vivien Killilea/Getty

A Life-Changing Call from Leonardo DiCaprio

Ladkani was busy working on a script for a feature film in August 2017 when DiCaprio, one of the world’s foremost environmental champions, called.

The two got to know each other after working on the undercover 2016 Netflix documentary, The Ivory Game, about the gruesome slaughter of elephants in Africa by illegal poachers for their tusks, leading them down the path of extinction as well. (The film led China to ban on the centuries-long sale of ivory in 2017, Deadline reported.)

"He basically asked if I could drop everything and go help save the vaquita," says Ladkani. "I was like, ‘Excuse me? What animal?' I had never heard of a vaquita in my life."

“But if we can’t save this tiny little area — 20 by 20 miles in the Sea of Cortez where the vaquita live, how can we save anything in this world?" he asks.

“It’s quite a complex issue,” Ladkani says. “But I am optimistic that we can overcome it.”

Fearless Eco-Warriors on the Front Lines

The film starts out showing the intrepid young crew of The Sea Shepherd as they try to catch poachers in the middle of the night with the use of a drone that captures their every illegal move.

“What I really love is that we have these heroes, like [drone operator] Jack Hutton, who are fighting evil,” he says. “He’s 22 years old. He the new future of our planet. For me, he is a superhero. He is an Avenger for the planet — literally out there fighting the cartels right now.

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Jack Hutton of The Sea Shepherd investigates a dead totoaba with two Mexican navy officers standing guard in Sea of ShadowsNational Geographic

Other heroes in the film: Dr. Cynthia Smith of the National Marine Mammal Foundation, who tries to save the vaquitas in a daring operation, VaquitaCPR.

One of the most heartbreaking scenes comes when she and her team try to help a female vaquita.

“That was very difficult to film,” says Ladkani.

RELATED: Teen Climate Activist Greta Thunberg Blasts World Leaders at the UN: 'How Dare You!'

The film also follows Mexican investigative journalist Carlos

Leo DiCaprio’s Nat Geo Thriller Exposes How Quest for 'Cocaine of the Sea' Kills Rare Vaquita_3
Investigative journalist Carlos Loret de Mola trying to connect Mexican poachers to Chinese traffickersNational Geographic

Loret de Mola, who goes in-depth on the divisive issue.

It also features Andrea Crosta, founder of Earth League International, a group of former intelligence, law enforcement and security professionals who are working to save wildlife, according to its website.

The Sea Shepherd and Earth League International “are our first — and last — line of defense,” he says.

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The Sea Shepherd vessel in the coastal waters of San Felipe in Mexico, trying to keep poachers awayNational Geographic

Other groups left because they were afraid, he says. “These two that are still on the front lines are amazing,” he says.

A Mentor of Mentors

When things get hard for Ladkani, he thinks of his mentor, legendary primatologist Jane Goodall, whose own tireless journey to save wildlife inspires him to keep going.

“She taught me that everything in this world is connected to everything else. In the ocean you can't just have a species disappear and think it’s okay," says Ladkani.

“We are part of that as well," he adds. "We can't ignore that. We have to fight for it.”

In an exclusive clip from the film given to PEOPLE, Goodall says people often ask why it matters if one species dies.

"There are examples where the loss of one seemingly insignificant species eventually, through a ripple effect, can lead an entire ecosystem to collapse," she says. "We don't completely understand the interconnectedness of all living things so this little vaquita – so beautiful – I had never heard of it before I was introduced to it in Sea of Shadows – what a charming face. And the fact that they are almost extinct is sad."

Ladkani hopes people watch the documentary and take action by sharing the film on social media, donating to nonprofit organizations The Sea Shepherd and Earth League International, and signing their petition on their website.

Why? “This story is a symbol of what is happening in the world,” he says. “In the Sea of Cortez, you everything that is wrong with our world."

“What I get very emotional about is that you have these criminal syndicates that are making millions of dollars by killing endangered species and sending them off to markets — mostly to China,” he says.

“You have the same stories about the black market in the Amazon, with illegal logging; in Africa, with the rhinos; and in Asia, with the tigers," he says. "These animals are dying at such a fast rate and these criminals are making millions of dollars — and people are not even aware."

“We can change this.”