The River Dee is a nationally and internationally important river, designated as a Special Area of Conservation and protected under UK and European environmental law. Despite these protections, raw sewage continues to be discharged into its waters. Across the Dee catchment, 40 major wastewater treatment works release effluent into the river, the majority of which are owned and operated by Dŵr Cymru (Welsh Water). One of these major wastewater treatment works is located in Corwen, within the upper catchment of the Dee.
In Corwen, the sewerage network includes three permitted storm overflows. These are designed to discharge untreated sewage into the river during periods of exceptional rainfall to prevent sewage from backing up into homes and businesses. In 2025, these three overflows discharged into the River Dee for a total of 1,218.75 hours. It is difficult to argue that over 1,200 hours of sewage discharges are solely the result of exceptional weather, suggesting the system is regularly being overwhelmed.
This volume of pollution will have a direct impact on the water quality and wildlife of the River Dee. While responsibility for these discharges lies with Dŵr Cymru (Welsh Water), the Dee Trust has been working hard to find ways to reduce raw sewage entering the river wherever possible.
Many older sewerage networks, including the one in Corwen, operate as combined systems. This means the same underground pipes carry both household wastewater (from toilets and sinks) and surface water runoff from roofs, roads and other hard surfaces. During heavy rainfall, the additional volume of water can overwhelm the system, increasing the likelihood of sewage discharges into the river.
To help tackle this problem, the Dee Trust will be installing sustainable rain garden planters within Corwen through our It Shouldn’t Be in the Dee programme. These rain gardens are strategically placed in locations where they can intercept rainwater before it enters the sewerage network.
A rain garden planter is a nature-based feature that captures and slows rainwater falling on roofs before it enters drains. By temporarily storing water and allowing it to soak away more slowly, rain gardens help reduce pressure on drainage systems and lower the likelihood of sewage overflows.
By installing rain gardens across Corwen and the wider Dee catchment, we can help capture and slow rainwater before it enters drains and sewers. This helps wastewater treatment works operate more effectively by preventing them from becoming overwhelmed and should help reduce the frequency of raw sewage entering the River Dee.
While the scale of the problem can feel overwhelming, rain garden planters provide a practical, community-led solution that can make a real difference.
The rain gardens in Corwen have been installed as part of the Nature Networks Fund-funded Restoring the Dee Together project.
If you would like to keep up to date with our work, make sure to follow the Dee Trust on social media.
