Nurdles are very small plastic balls. The plastic industry uses them to make bigger plastic things like bottles and bags.
A group called Fidra checked special nature sites in the UK. These sites protect rare animals and plants.
They found nurdles in 84% of the sites. That is 168 out of 195 places.
Nurdles are also in six national parks. These are Loch Lomond and the Trossachs, North York Moors, New Forest, Pembrokeshire Coast, Eryri or Snowdonia, and South Downs.
The worst places are River Itchen in Southampton and Firth of Forth in Scotland.
Factories make nurdles in places like Grangemouth in Scotland. They send them by truck and ship.
Sometimes nurdles spill by accident. Experts think up to 53 billion spill in the UK each year.
Nurdles have toxic chemicals. They are bad for nature.
Animals think they are food. They eat them and get sick. Nurdles break down into microplastics. These go into our food.
Megan Kirton from Fidra says: 'It is shocking. Special nature places have plastic pollution. We can stop this.'
Fidra wants new rules. Governments must stop spills. They want safe ways to move nurdles by sea and land.
Fidra asks for world rules on nurdles. They want laws to make companies careful. The International Maritime Organization must help too.