Sewage, agriculture, climate change, microplastics and pharmaceuticals appear to have slowed the biological recovery of rivers in England and Wales, new research suggests.

A study of invertebrates that live on river beds found their numbers had increased by nearly 10% from the early 1990s until 2018 for more pollution-sensitive species, but their recovery has since waned.

Researchers from Cardiff University analysed nearly 50,000 invertebrates collected from around 4,000 streams and rivers.

Emma Pharaoh, a PhD researcher from the university’s School of Biosciences, said: “Invertebrates are important indicators of river health, reflecting pollution and other human impacts.

“By looking at the types of invertebrates living on the river bed, we can get a good picture of river health.

“Up to 2018, the number of invertebrate families in our rivers increased by nearly 10% and communities were comprised of more pollution-sensitive invertebrates.

“We also found that despite urban rivers historically being the most polluted, they showed the greatest improvements – taking them closer in quality to rural rivers.”

Last year, sewage was dumped into UK waterways on more than 300,000 occasions, a drop from the previous year but only because of exceptionally dry weather, the Environment Agency said.

The Government has said it is making water companies invest £56 million into improving the infrastructure to reduce pollution and that awareness of the scale of the problem is because of more improved monitoring.

Despite the recent recovery slowdown, the broader trend since the 1990s has been positive, the researchers of the current study said.

Dr Ian Vaughan of Cardiff University’s School of Biosciences said: “These results represent a positive story about rivers, against a background of often bad news.

“With ongoing issues including water quality and climate change, rivers face many challenges. These results highlight how biodiversity can recover if environmental quality is improved.”

The study used data from the Environment Agency and Natural Resources Wales (NRW) and updated a 10-year-old analysis from Cardiff University, which allowed the researchers to investigate trends over decades.

Ceri Davies, executive director of evidence, policy and planning at NRW said: “While we have made good progress in protecting and enhancing our waters over recent decades, this study is a stark reminder that there is still a long way to go.

“The challenges facing our rivers may evolve with time, but the need for concerted and collaborative action to conserve them remains.

“Now is a pivotal time for change, not complacency, and an opportunity to once again accelerate improvements to our rivers.”

Professor Steve Ormerod of Cardiff University’s School of Biosciences and Deputy Chairman of Natural Resources Wales added: “Urban river improvements since the early 1990s reflect the combined effects of industrial decline, improved regulation and investment in wastewater treatment.

“But hints of a more recent slowdown show how we need further action – especially from regulators, water companies and agriculture – to regain and maintain the positive trends.”