Therese Coffey is facing calls to resign after figures showed water companies dumped sewage into waterways over 300,000 times last year.
Lib Dem leader Ed Davey said it was a “national scandal” and accused the environment secretary of ignoring “environmental crimes” on her watch.
“Therese Coffey must now resign or be sacked so we can have an environment secretary who actually cares about saving our rivers from destruction,” he said.
“Her plans to solve this crisis would allow sewage dumping to happen for decades to come, poisoning more animals and destroying precious chalk streams.”
Data from the Environment Agency showed sewage was spilled 301,091 times in 2022, equivalent to 824 times every day.
This is lower than the 370,000 spills in 2021, but the agency said this was due to dry weather, not the actions of water companies.
Pop star and environment campaigner Feargal Sharkey also backed the calls for Coffey to resign.
The Lib Dems have made tackling sewage a key part of their local election campaign.
Speaking at the party’s spring conference earlier this month, Davey predicted it would cost the Conservatives “dozens of seats” at the next general election.
The party also made water pollution a central part of its successful bid to overturn a huge 24,000 majority at the Tiverton and Honiton by-election last June.
Figures recently revealed that pay and bonus packages for water firm bosses soared by a fifth in 2021-22, despite significantly sewage spills in Britain’s waterways.
The average pay for executives at 10 firms across England and Wales jumped to £1.1 million in 2021-22, up by £193,000 on average.