Seth Orme, 26, and Paul Twedt, 30, have carried everything from beer bottles and cigarette butts to discarded mattresses for stretches of up to 100 miles – just to find a proper place to dispose of them.

Driven by a love of the outdoors, these two young Americans are hiking famous US trails and picking up every bit of litter that they see along the way.

The pair hiked the Appalachian Trail in 2015 with their friend Joe, picking up 1,100lbs of rubbish on their four-and-a-half-month journey and recycling items whenever they could.

This year, as part of their mission, which they call “Packing It Out”, the pair spent five months clearing the Pacific Crest Trail from the border with Mexico up to British Columbia in Canada.

Seth had been working as an outdoor guide, including a stint as a kayak guide on Lake Superior, and spent most of his younger years outdoors.

Seth Orme hikes with rubbish on his back until he can find a proper place to dispose of it (Packing It Out)

“When I was 19 I kayaked all 2,500 miles of the Mississippi River, and that started me thinking that I wanted to invest more of my life in the outdoors,” he says.

“When you work in the outdoors, you get to the point where you’re sleeping more outside than inside, and the outdoors becomes your home. And like any home, I wanted to keep it clean, so it became a habit.

“It was a habit I wanted to share, and influence other people’s values. We don’t want to have trash all along our scenic trails. I thought, ‘How can I inspire people to pick up their trash?’ So I set the bar really high and decided to do something audacious, and hoped it might inspire people.”

The pair’s plans are getting bolder. By 2018, Seth hopes to take Packing It Out outside the US.

But first, with various outdoor clothing and organic food companies now serving as sponsors, their next big litter-clearing mission will cover some 2,500 miles from Cumberland Island in Georgia, in the south-east of the US, to the Olympic Peninsula in Washington State, in the opposite corner of the country.

From April next year Seth and Paul will travel the route by bike, cleaning up rivers and trails as they go. As with previous hikes, they’ll be camping.

“You sleep on the ground outside, either in the tent or we decide to do cowboy camping, where you just lay down on the ground and go to bed,” says Seth.

The guys find all sorts of trash on their travels, including abandoned toys (Packing It Out)

“We just do it because we love the outdoors. We haven’t had any bad feedback. Sometimes people are confused – they wonder why we’re picking up more weight when you’re not supposed to pick up more weight when you’re going a long distance.”

Seth says the people they meet along the way are generally open and interested in what they’re doing, often inviting the pair into their homes for showers and hot dinners and the occasional bed for the night.

But is all their hard work paying off? Seth went back again recently to hike one of the stretches of the Appalachian Trail where they found the most rubbish, near where he now lives in Asheville in the Appalachian Mountains, and found it was “significantly” cleaner.

If you arrive at an area that is super-clean, his argument is you’re not going to leave any rubbish. “If you go to someone’s home and it’s really clean, you’re like, ‘I’m not going to throw trash on their floor.’ I hope people will start seeing the outdoors as less of a commodity and more of a community that we respect and value.”