The reports published here set out in detail the Office for Environmental Protection’s findings from our investigation into the regulation of combined sewer overflows by Defra, the Environment Agency and Ofwat.
Our investigation found that there had been failures to comply with environmental law by each of the three public authorities relating to the regulation of network CSOs. Decision notices were issued to them setting out the actions required to address the non-compliances. We welcomed responses from them which showed positive action to address the concerns raised and significant progress being made.
We announced in July 2025 that we were to conclude our investigation after securing significant progress in tackling the issues we identified. These reports set out the findings behind this decision, and make further recommendations to strengthen regulation and prevent reoccurrence of the failures identified.
Please find the three investigation reports using the blue buttons on the right hand side of this page. Below the reports you can find the decision notices and information notices we sent to each public authority as part of our enforcement activity.
