Did you know there is a river flowing underground through the centre of Bristol? Find out more about the history and wildlife of the River Frome and take yourself on BART’s Secret River Trail to follow the underground river.
The Secret River Trail launched on 7th June 2025 as part of the Festival of Nature. Until 15th June, 200 painted fish will guide you along the route of the trail. We invite you to walk the streets of Bristol where a river is flowing beneath your feet.
The River Frome is a 20 mile stretch of river starting in Dodington Park, South Gloucestershire, flowing southwards into Bristol, and eventually flowing into the River Avon.
What is now mostly an invisible river in the centre, was once part of a large, busy working harbour; the space in front of Bristol Hippodrome was once all open water with bridges connecting each side of the city! Nowadays most people walk on top of the river without even realising its existence.
It wasn’t until 1858 that the Frome was culverted to flow underground, to allow further development of the centre. Not only that, but sewage was deposited into the Frome, which would then sit in the harbour and fester. Culverts were built so that the sewage could flow into the New Cut of the River Avon.
Whilst the culverts helped develop the city and were great for diverting sewage, they were bad news for river wildlife. The smooth flat surfaces and dark tunnels make it difficult for plant life to colonise. Fish do not like navigating through dark spaces and find it difficult to swim up smooth concrete surfaces.
In addition to the culverts, there are many man-made barriers such as weirs, which prevent the movement of migrating fish, as they find it difficult to move over these large barriers. There are over 15 weirs on the River Frome, and dozens more barriers across river and its catchment.
However, there are populations of critically endangered European eel in the Frome – eels can sometimes cope better with navigating these dark tunnels and are even able to climb wet surfaces like rocks!
Despite all this, there are great pockets for wildlife along the River Frome, such as Eastville Park, Oldbury Court, and Black Rocks.
The River Frome is designated as a Site of Nature Conservation Importance (SNCI), along its main channel. There are many notable species such as stream water-crowfoot, brown trout, European eel, branched burr-reed, and meadowsweet.
The Bristol Frome is sometimes Bristol’s forgotten river. We hope you enjoy this fascinating and often beautiful river that provides enriching blue space in the city for both people and wildlife. That is, when it’s not underground!