A new study examining nitrogen pollution in the Mersey Estuary over the last 200-years has found concerning levels of sewage in the water today – and our experts say immediate action is needed to clean it up.

The River Mersey, in north-west England, was once dubbed the most polluted river in western Europe.

And new research by geochemists Freya Alldred and Professor Darren Gröcke has found that despite previous efforts to clean it up, the river and its estuary remain heavily polluted by sewage nitrogen.

The researchers used herbaria – dried seaweed – from the collection at the World Museum, National Museums Liverpool, to investigate nitrogen pollution in the Mersey Estuary over the past 200-years.

Herbaria act like time capsules, capturing in its tissues the environmental conditions it was growing in.