"This is a planetary crisis... we are ruining the ecosystem of the ocean," UN oceans chief Lisa Svensson told the BBC this week.
But how does this happen, where is most at risk and what damage does this plastic actually do?
Plastic as we know it has only really existed for the last 60-70 years, but in that time it has transformed everything from clothing, cooking and catering, to product design, engineering and retailing.
One of the great advantages of many types of plastic is that they're designed to last - for a very long time.
And nearly all the plastic ever created still exists in some form today.
In July a paper published in the journal Science Advances by industrial ecologist Dr Roland Geyer, from the University of California in Santa Barbara, and colleagues, calculated the total volume of all plastic ever produced at 8.3bn tonnes.
Of this, some 6.3bn tonnes is now waste - and 79% of that is in landfill or the natural environment.
This vast amount of waste has been driven by modern life, where plastic is used for many throwaway or "single use" items, from drinks bottles and nappies to cutlery and cotton buds.
Drinks bottles are one the most common types of plastic waste. Some 480bn plastic bottles were sold globally in 2016 - that's a million bottles per minute.
Of these, 110bn were made by drinks giant Coca Cola.
For sea birds and larger marine creatures like turtles, dolphins and seals, the danger comes from being entangled in plastic bags and other debris, or mistaking plastic for food.
Turtles cannot distinguish between plastic bags and jellyfish, which can be part of their diet. Plastic bags, once consumed, cause internal blockages and usually result in death.
Larger pieces of plastic can also damage the digestive systems of sea birds and whales, and can be potentially fatal.
A recent survey by Plymouth University found that plastic was found in a third of UK-caught fish, including cod, haddock, mackerel and shellfish.
This can result in malnutrition or starvation for the fish, and lead to plastic ingestion in humans too.
The effect on humans of eating fish containing plastic is still largely unknown.
But in 2016 the European Food Safety Authority warned of an increased risk to human health and food safety "given the potential for micro-plastic pollution in edible tissues of commercial fish".