Targets for 75% of rivers to be healthy by 2027 are "very unlikely" to be met in England, a charity has warned.
The World Wide Fund for Nature (WWF) says rivers are "used as open sewers".
The Environment Agency predicts 75% of rivers in England and along the Scottish and Welsh borders will meet EU expectations by 2027, compared with just 14% now.
It is planning an autumn consultation on "challenges and choices" faced in cleaning up water.
The agency said it would review the target based on "what can realistically be achieved".