One of Netflix’s ‘best ever’ documentaries left viewers in tears after learning about one of the deadliest activities in the world

A documentary that hit Netflix two years ago is still having an effect on viewers as they hail it the 'best ever' thing they've watched and admitted to being in tears.

Netflix has become something of a pioneer in the documentary department - from true crime to our favourite celebs - having developed a knack for the genre over the years.

But there's one documentary on its lengthy roster that viewers say stands out above the rest, and it even bagged an Emmy last year to prove it.

It took home the gong for Outstanding Long Sports Documentary, with viewers praising it as 'mesmerising' and a 'must watch', and others saying it left their 'heart shattered'.

Freediving is extremely dangerous (Netflix)

Written and directed by Irish filmmaker Laura McGann, The Deepest Breath explores the ins and outs of competitive 'freediving' and the tragedy at the heart of it which ripped through the community in 2017.

Freediving is a dangerous extreme sport where competitors attempt to dive to mind-boggling depths underwater without any scuba gear, meaning they literally hold their breath the entire time until resurfacing.

Athletes will train intensely as they hope to secure new records in the depths of the ocean, but of course, it's an extremely dangerous sport due to the length of time you are required to hold your breath and the water pressure your body is subjected to at such depths.

At the heart of the documentary - billed by Netflix as a 'perilous undersea love story' - is Italian champion Alessia Zecchini and Ireland’s Stephen Keenan, with Zecchini hoping to set a new world record assisted by Keenan, who is a safety diver.

Safety divers like Keenan are a necessity as freedivers can often have blackouts during their ascent to the surface after holding their breath for so long.

In The Deepest Breath, Zecchini and Keenan adorably fall in love during their quest for the sporting record, as the doc follows their attempt at the dangerous feat as well as explaining the mechanics of the sport and the risks involved.

The nearly two-hour-long film shows us how pair train together as the Italian prepares to take on the legendary Blue Hole in Dahab, Egypt - a challenge which will see her dive 184 feet below the Red Sea and swim through an 85-foot-long tunnel to the safety rope on the other side.

Viewers said it left them in tears (Netflix)

Here, she is supposed to be met by Keenan. However, it all goes tragically wrong.

After watching the gripping documentary, fans were quick to share their opinions on Twitter, as one branded it 'wild' and others called it 'very emotional'.

One wrote: "This afternoon I watched The Deepest Breath on Netflix. As a former dive instructor who tried a bit of free diving, I found it very emotional.

"One of my instructors, Nico, died while freediving back in 1998. RIP to all those lost to the sea."

Meanwhile, another commented: "That doccie was amazing. Heartbreaking. Beautiful. Sad. Poignant. Touching. Eye opening."

The Deepest Breath is available to stream on Netflix now.