More than two million tonnes of throwaway plastic soft drinks bottles are sold each year, with only a small proportion made from recycled materials, research reveals.
A survey by Greenpeace found five of six global soft drinks firms sold single-use plastic bottles weighing more than two million tonnes or the equivalent of 10,000 blue whales each year - only 6.6% of which was recycled plastic.
If figures from Coca-Cola, which did not disclose how many tonnes of plastic it sells, were included, the numbers would be much higher, the campaigners said.
Single-use drinks bottles are a visible part of the problem of plastics pollution in the world's oceans, forming the most common type of plastic packaging found washed up on shorelines globally, Greenpeace said.
Millions of tonnes of plastics are ending up in the ocean every year, harming marine wildlife, taking centuries to break down and spreading toxic chemicals.
Greenpeace wants soft drinks brands to do more to tackle marine plastic pollution, for example by producing more 100% recycled bottles and committing to phasing out the use of throwaway plastic.
Louise Edge, senior oceans campaigner at Greenpeace UK, said: "We know that plastic bottles are a huge ocean-polluter and in the UK alone we dump 16 million of them in our environment every day.
"If we're going to protect our oceans we need to end the age of throwaway plastic.
"Companies need to move away from single-use plastic, embrace reusable packaging and make sure the rest is made from 100% recycled content."
Companies responding to the survey are taking action including reducing plastic by making bottles thinner or using bioplastics which are not made from oil, and removing "problem plastics" to make them more recyclable.
But Greenpeace said lighter and bioplastic bottles still contributed to marine pollution, and did not compensate for the growth in the total volume being produced.
There was also a move away from refillable bottles, low levels of recycled plastic used in drinks containers and opposition to deposit return schemes which pay people to return empty bottles, according to the green group.
The firms surveyed by Greenpeace were Coca-Cola, PepsiCo, Suntory, Danone, Dr Pepper Snapple and Nestle.
British Soft Drinks Association director general Gavin Partington said: "We should all be concerned about the problem of marine litter.
"All plastic bottles are 100% recyclable so it is important that consumers are encouraged to dispose of bottles responsibly.
"However, we recognise more needs to be done to increase recycling and reduce littering.
"We want to work with campaigners, central and local Government and other companies in the supply chain to support action that achieves these aims."
A Coca-Cola Great Britain spokeswoman said: "For decades we have actively supported recycling programmes, anti-litter campaigns and ocean clean-up, but it is clear more action is needed.
"That's why last year we began a review of our sustainable packaging strategy and recently agreed to support the trial of a well-designed deposit return scheme in Scotland to understand whether it will help to improve recycling rates and reduce litter."
The company has reduced the amount of packaging by 15% since 2007 in Great Britain, and its bottles in the country contain 25% recycled material.
It will also publish new sustainability plans in June.