Holidaymakers cause a 40% spike in marine litter entering the Mediterranean Sea each summer, and the vast majority of it is plastic, a report warns.
Around 95% of the waste in the open sea, on the seabed and on beaches across the region is plastic, with the majority coming from Turkey and Spain, followed by Italy, Egypt and France, the study by wildlife charity WWF said.
The Mediterranean is one of the seas with the highest levels of plastic pollution in the world, with hundreds of thousands of tonnes of plastic items and tiny "microplastics" ending up in it each year and harming wildlife.
More than 200 million tourists visit the Mediterranean each year, including millions of Britons, causing the 40% increase in marine litter during summer, according to the report released to mark World Oceans Day.
The conservation charity is calling on holidaymakers to look at cutting down on single use plastics including straws and stirrers, drink tap water where it is safe to do so, and avoid items such as disposable inflatable pool toys.
Other tips for tourists to cut down on plastic include bringing a bag for life on holiday, freshening up with mints instead of gum, using a washable cloth not face wipes, and ensuring they take any rubbish with them off the beach.
Europe is the second largest plastics producer in the world, after China, and dumps the equivalent of 66,000 rubbish trucks of large plastic pieces such as bottles and carrier bags into the sea.
These items can suffocate and injure marine animals or be mistaken for food and eaten by species such as fish and turtles, who then suffer blockages, starvation and internal wounds leading to their death.
Though it contains only 1% of the world's water, the Mediterranean is a semi-enclosed sea with lots of human activity and as a result is a "plastic trap" where 7% of all the world's microplastic waste is found, WWF said.
These tiny pieces of plastics can also be eaten by fish or other creatures such as mussels which can then end up on holiday seafood dinner plates.
On average someone eating fish in Europe could be ingesting up to 11,000 pieces of microplastic a year, the report warned.
Tanya Steele, chief executive at WWF, said: "The Mediterranean is a beautiful holiday destination enjoyed by millions of British people each summer but when we come home with our happy memories, we're leaving behind a toxic legacy of plastic waste.
"The birds, fish, and turtles of the Mediterranean are choking on plastic, but our report also shows plastic is ending up in the fish and seafood we eat on holiday.
"That's why we're asking people to think about how they can cut down on the amount of single-use plastic they use and throw away on holiday.
"By drinking tap water where it's safe to do so, refusing plastic straws and stirrers or skipping the disposable inflatable pool toy, we can all be part of the solution and not the problem."
The Mediterranean is home to almost 25,000 plant and animal species, almost two thirds of which are unique to the region, with wildlife ranging from loggerhead turtles to tuna and swordfish swimming in the seas.
But many species of fish, marine mammals, turtles and seabirds have eaten plastics, including crisp packets and cigarettes found in fish, and one sperm whale found washed up with metres of fishing line and flexible hose, two flower pots and several plastic tarpaulins in its stomach.