Thirsty while running? Here, have a seaweed ball full of sports drink.

More than 41,000 people will run the London Marathon on Sunday. When they reach mile 23, they'll be handed edible pods made of seaweed extracts instead of a plastic water bottle.

It's one way race organisers are hoping to reduce the huge amount of plastic waste generated during the endurance run. They want to cut the number of plastic bottles used by 200,000.

The Ooho seaweed capsules are made by a London-based startup called Skipping Rocks Lab.

They can be cheaper to produce than plastic and the thin membrane that forms the pod is edible and tasteless.

"What we use is the building blocks of seaweed," said Rodrigo Garcia Gonzalez, one of the startup's founders. "We remove all the green stuff and the smelly stuff," he added.

The pods biodegrade within six weeks if they're not eaten — a far cry from the 450 or more years it takes a plastic bottle to decompose. Sunday's race marks the first time they'll be used at a marathon.

"The marathon is a milestone ... we are hoping we will demonstrate that it can be used at scale in the future," said Garcia Gonzalez.

The pods are meant for people on the move, such as runners and music festival attendees. They can be filled with a variety of liquids.

"Espresso Martinis have been the most popular product at festivals, where eating the packaging is also part of the experience," said Pierre-Yves Paslier, Garcia Gonzalez's business partner.

The duo met while studying innovative design engineering in London. They say the mission of their company is to "make plastic packaging disappear."

In addition to liquid pods, they are also working on green alternatives to cling film and the plastic liners used in throwaway coffee cups.

The startup is working to develop machines that can produce the capsules at scale, with a view of leasing them to companies that want to use them to package their drinks or other products, like sauces.

Doing so could help solve one of the world's most pressing environmental challenges: Plastic.

According to a 2017 study published in the journal Science Advances, only 9% of 8,300 million metric tons of plastic ever produced has been recycled. Another 12% has been burnt in incinerators.

The remaining 79% has been sent to landfills, improperly discarded or found its way into the oceans.

Producing plastic bottles also requires a lot of energy and water. It takes more than five liters of water to produce a standard 500 ml plastic bottle, according to advocacy group Water Footprint Network.

London Marathon organisers are taking other steps to make this year's event more sustainable.

Energy drinks will be served in compostable cups at two other drink stations, reducing the total number of plastic bottles used from 920,000 in 2018 to 704,000 this year.

All water bottles handed out this year will be at least partially made of recycled plastic, and the discarded containers will be recycled.

Hugh Brasher, the event director, said London Marathon wants to be leading the way in sustainability.

"The changes and the trials we're introducing for this year have the potential to change how mass participation events are delivered in future," he added.