Environment Agency data shows serious pollution incidents were up 60% last year.
Southern, Thames and Yorkshire Water were responsible for 81% of those.
A recent diesel spill of 4,000 litres polluted the River Wandle in Thornton Heath, triggering an urgent cleanup.
Singer and fresh water campaigner Feargal Sharkey says the government needs to step up:
Environment secretary and MP for Streatham and Croydon North, Steve Reed, says ministers are making one of the sector’s biggest ever investments in infrastructure.