Drop a plastic bottle into the Ganges and where does it end up? An all-female team of engineers, explorers and scientists is about to find out by undertaking the first expedition to measure plastic waste in one of the world’s most polluted waterways.

Following the Ganges upstream from where it empties in the Bay of Bengal to its source in the Himalayas, the National Geographic-backed expedition aims to better understand how plastic pollution travels from source to sea and provide solutions for reducing the amount that ends up in the world’s oceans.

The 2,525 km-long Ganges is a river of extreme paradox: though worshipped by 1 billion Hindus and relied on as a water source for roughly 400 million people, it is contaminated with industrial runoff, untreated sewage and household waste. It is also one of 10 rivers responsible for 90% of the plastic that ends up at sea.

The river is, therefore, a perfect starting point for measuring how plastic travels from land into rivers, and from rivers into the ocean, says National Geographic fellow and University of Georgia associate professor Jenna Jambeck, who is co-leading the expedition.

“We know there’s plastic in these river environments and that the plastic is heading into the ocean,” says environmental engineer Jambeck, whose previous research found that 8m metric tons of plastic waste enters oceans every year.

“But we don’t know how far, for instance, if someone dropped a plastic bottle into the Ganges, where it ends up. How far does it go?”

The team of 18 – with researchers from organisations including the Wildlife Institute of India, University of Dhaka and Zoological Society of London (ZSL) – completed the first round of the expedition this spring to collate pre-monsoon plastic levels.

In October, the team will take two months to retrace the same route, travelling up and around the Ganges by boat, road and train, collecting post-monsoon pollution levels in the air, water and sediment, and in species in and around the river. Local and national responses to managing pollution will also be compared, as will communities’ interactions with, and dependence on, the waterway, said marine biologist and expedition co-lead Heather Koldewey.

“‘The plastic is everywhere’ story is well told now – what really matters is what we can do about it,” says Koldewey, who is a National Geographic fellow and ZSL advisor.

Heather Koldewey, co-lead of the Sea to Source: Ganges expedition , examines a sample from the river.

“A big part of our work is looking at the connection between plastic and poverty, as plastic has given people access to so many products that they wouldn’t have previously been able to get, whether that’s food packets or shampoo sachets. But the environmental consequences of that has been enormous.”

Taking samples from the Ganges (seven miles at its widest) can be difficult, added Koldewey, with tidal waves causing seasickness and plastic waste present at nearly every point along the river, ranging from plastic bottles and carrier bags to plastic religious offerings.

“This expedition is a proper adventure: the Ganges is so wide at times that you can’t see the other side – it’s like being in the ocean – and we travel all the way up through Bangladesh into India to the [Gangotri] glacier, the source of the river where the ice melts, which is retreating several metres every year due to global warming.

“We’ve been tracking the litter we found using an open-source app designed by the University of Georgia, and are working with a drone pilot along the riverbanks to trace how plastic gets into the river from the land. We also made some wooden drift cards to see how litter moves through the river system, which have messages in Bangla and Hindi on them asking people to report into us when they find them.”

The team also placed a tracking device inside a plastic bottle, similar to those used on sharks and turtles, and set it adrift into the Ganges to determine how far downriver it goes.

An aerial view of Hindu devotees in the water at the intersection of the Yamuna and Ganges rivers. Photograph: Rajesh Kumar Singh/AP

“The idea was that it could end up at sea,” said Koldewey. “The device pings to a mobile or satellite signal so we know where it is at all times and will collect it at the end of our expedition.”

Ethically, the team debated whether or not to use plastic devices to track plastic pollution, she added, but concluded that it was necessary for collating data. As a rule, any plastics that the team are bringing into Bangladesh and India they are taking out with them again, whether that’s toiletries, medical packets or technology, said Koldewey.

The Ganges was chosen as the first of several river expeditions planned for National Geographic’s Planet or Plastic? initiative, which aims to reduce single-use plastic waste entering the world’s seas.

“These expeditions are a tremendous opportunity to mobilise a global community of experts to help tackle the problem,” said Valerie Craig of the National Geographic Society.

“I’m particularly delighted that this expedition elevates women in science, technology, engineering and maths around the world to help us understand how plastic moves through our waterways and ultimately to find ways to prevent plastic waste from entering the ocean.”

In 2002, Bangladesh was the first country in the world to ban single-use carrier bags – but plastic comprises 8% of the nation’s waste every year. In India, Narendra Modi has pledged close to $3bn (£2.47bn) for a clean-up of the Ganges, due for completion next year. Yet only a fraction of the budget has been spent, official figures show, and in many parts of the river, levels are more polluted than when the cleanup began in 2015.

Nevertheless, both Jambeck and Koldewey are hopeful that the data they collect will make a positive difference, as the National Geographic team are focusing on building solutions and filling gaps with local and national partners and creating long-term change.

“We’re not trying to demonise plastic – it has a huge role in society – but when you look at the impact of its waste, when there’s no infrastructure to deal with it or the infrastructure is weak, it is causing huge consequences, whether that’s on people, animals, wildlife or the health of the river system,” said Koldewey.

“Having worked on plastic pollution for many years, what’s encouraging for me is seeing in the last two or three years a real groundswell of movement. It really feels like there is now energy and time for change, as there is ambition at the top levels of government, and that enables many groups to make change themselves.”