It was a moment explorer Brian Skerry will always remember... saving the life of a whale caught in a fishing net.
Then in his early 20s, Brian had just come up from exploring a shipwreck off Cape Cod Bay in the U.S. when a lobster fisherman asked for help.
I could have been killed, but like an idiot I just jumped back into the water with a knife in my hand, recalls Brian.
I then spent about an hour or two cutting that whale out. I remember, as I cut that last piece of line, that young humpback whale looked at me with its big eye, then just rested for a few moments and swam away.
I was hooked. Theres something very special about being in the water with whales.
This incredible experience sparked a lifetime interest in the creatures for Brian, now 59, who grew up in a small town in Massachusetts and always dreamed of exploring the ocean.
Dreams do come true, says Brian, who now works as a National Geographic photographer specialising in marine wildlife.
Im very lucky to do what I do every trip and assignment you go on, you come back having learned something new, he said.
Its allowed me to travel all over the world and come close to amazing creatures. I never take my job for granted.
After doing a cover story for National Geographic in 2015 on dolphin intelligence, Brian decided he wanted to work more with whales and dolphins.
Now his dream is being realised, as hes one of the stars in new documentary series Secrets Of The Whales.
Produced by Titanic director James Cameron and narrated by Alien actress Sigourney Weaver, the series is a four-part epic that takes viewers into the secretive world of five different whale species orcas, humpbacks, belugas, narwhals and sperm whales.
The show examines the communication skills and social structures of these breeds, teaching viewers that the animals are more like us than we could ever imagine.
Secrets Of The Whales took three years to film and saw Brian and the rest of the crew venture to 24 locations including Iceland, Antarctica and Sri Lanka.
It launches on Wednesday to tie in with Earth Day on Thursday, a worldwide event to raise awareness of the need to protect the environment.
And Brian hopes viewers will be inspired to make changes in their day-to-day life to help the natural world. Theres 18 billion pounds of plastic going into the ocean every single year and that doesnt have to happen, he said.
We live on a water planet. The majority of areas on Earth where life can exist is water.
So its in our best interest to protect it. The more people know about it, the better we will be at recognising the importance of looking after the ocean.
Even if you dont live anywhere near the sea, you can still help protect the environment.
Simple measures to reduce environmental damage include being aware of what youre buying, avoiding single-use plastics, writing to manufacturers to encourage them to recycle products, eating seafood that is caught sustainably or reducing your meat intake.
Brian said: If everyone does something small, it can have a huge impact.
It can be overwhelming to think about the environmental problems in the whole world, but if we work together collectively to change things the planet will be OK.
One of the standout moments for Brian was when an orca tried to offer him a ray as a meal, mistaking him for another whale in their pod.
You could wait a lifetime for something like that to happen, he said. This adult female orca emerged slowly behind me after dropping the ray, then came face-to-face with me and looked at me like she was saying: Are you going to eat that?
You cant have an experience like and not be changed. I didnt believe it was real.
Brian adds the Disney+ series is full of other firsts and surprises which have helped further marine biologys understanding of the species.
There were loads of other jewels that stood out, he added. We spent an hour with one baby sperm whale, which we saw nursing from her mum. It was the first time anyone had ever seen this happen.
We also captured baby beluga whales picking up stones and playing a game of catch with each other, and an orca funeral procession.
It was a real revelation that these animals have such deep emotions and such a sense of community.
After spending three years filming Secrets Of The Whales, I have learned I could easily spend the rest of my life just studying whales as theres so many great stories there.
All four episodes of Secrets Of The Whales will be able to stream exclusively on Disney+ from Wednesday.
By Natasha Wynarcyzk