MORE than 70,000 weirs, dams and other river barriers have been mapped across Britain, as conservationists warn they are a “huge problem” for wildlife and river health.

A new database compiled by environmental charity WildFish reveals today that there is an average of one manmade barrier for every 2.5km of waterway across 150,000km of rivers across Britain.

Manmade obstacles are eight times more prevalent than natural barriers such as waterfalls, which occur around once every 20km on average.

Many barriers are “old, redundant” installations serving no practical purpose, yet they prevent fish and wildlife from migrating, create areas of concentrated pollution and damage overall river health.

Some 674 rivers in England failed to achieve good ecological status in 2023 due to blocks to fish migration.

River blockages are also a driving factor in declines for four of the seven British freshwater species at risk of extinction — Atlantic salmon, European eel, allis shad and twaite shad.

WildFish data analyst Daniel Nixon said: “River barriers have long been a huge problem for wildlife, pollution, and river health, yet the issue has received little attention — perhaps due to a lack of comprehensive data.

“While the number of barriers is overwhelming, there is also real hope: when unnecessary barriers are removed, rivers typically respond quickly, with river flow restoring and fish returning to previously inaccessible reaches.”

WildFish head of science and policy Janina Gray said that Atlantic salmon make migrations of more than 1,000 miles, but “each and every barrier makes this already difficult journey even harder.”

The charity said the biggest hurdle to removing barriers is securing planning and legal permissions, which can take months or years, but once approved, a barrier can be removed in hours, often just for the cost of hiring a digger.