LONDON — Holding placards with slogans such as “stop the plop” and “cash, not excrement”, thousands of people marched in London on Sunday to demand a clean-up of Britain’s sewage. waterways clogged with sewage.

Organizers estimated that 15,000 people took part in the march along the Thames to Parliament, many wearing blue and waving blue flags to form a “human river”. Police did not give a crowd estimate.

The Clean Water March has been organized by groups ranging from Greenpeace and Friends of the Earth to British Rowing.

Water pollution has become an increasingly high-profile issue in Britain, drawing attention to climate change and the legacy of the privatization of Britain’s public services decades ago.

Private companies that provide both water and wastewater have failed to update their often Victorian infrastructure as populations have grown and demand has increased. Leaks are common, and during heavy rains, companies discharge their raw sewage into rivers, lakes and the sea. The number of discharges increased by more than 50% last year to a record 464,000 spills, according to the Environment Agency.

Pollution from agricultural runoff also fouls Britain’s waterways, and climate change is making the situation worse by bringing more intense rainfall.

Rower Imogen Grant, a gold medalist at the 2024 Olympics, said it was common for rowers to fall ill after training on the River Thames.

“I spend hours and hours on the water training in the rowing boats every day during my sessions, and I see diapers floating, plastic bags, foam along the pontoons on which we we coach… It’s just not good enough and something needs to be done. change,” she said.

Water companies say the sector regulator will not allow them to raise water bills enough to finance the improvements.

The Labor government, elected in July, introduced a bill aimed at strengthening regulations and imposing tougher penalties on water companies responsible for pollution. But protesters said more needed to be done.

Broadcaster Chris Packham, who was at the march, said Britain’s rivers were “some of the worst in Europe”.

“But I am hopeful, firstly because we know what we need to do and we have the technologies to do it. What we need to do is convince our new government to act more quickly,” he said.