A UK water company has been illegally releasing sewage near one of Europe’s largest dolphin habitats for at least ten years.

Welsh Water, has confessed to spilling untreated waste at multiple locations for more than a decade. The company’s actions have endangered protected species in the River Teifi and Cardigan Bay, exposing them to untreated sewage discharges for years.

The town of Cardigan in west Wales is home to one of the most problematic sewage treatment plants. Unfortunately, the outflow point from this plant spills into the Teifi estuary, which is supposed to be protected as a Special Area of Conservation (SAC).

This estuary is the habitat of Atlantic salmon, lamprey, and otters. From there, the sewage flows into Cardigan Bay, an important habitat for approximately 300 bottlenose dolphins.

The main reason behind water companies releasing untreated sewage is the use of a combined sewerage system that covers most of the UK. In this system, rainwater and wastewater travel through the same pipes before being treated at a sewage treatment works. During extreme weather, it’s permitted to release mixed wastewater into rivers and seas via storm overflow pipes to prevent system overload. However, investigations have revealed that water companies are using overflows to discharge sewage even in mild conditions, which is illegal.

Raw sewage discharges into English rivers occurred a staggering 825 times a day last year, according to data from the Environment Agency. Professor Peter Hammond, a former University College London professor and member of Windrush Against Sewage Pollution (WASP), discovered that the Cardigan plant almost never treated the required amount of sewage. It illegally spilled untreated sewage for a cumulative total of 1,146 days between 2018 and May 2023.

Welsh Water has admitted that up to 50 wastewater treatment plants are currently operating in breach of their permits. They claim to be working to resolve the issue while prioritizing plants that will help reduce customer bills. However, environmental groups dispute the company’s assertion that there is “no measurable environmental impact” from the Cardigan estuary spills.

Untreated sewage discharges have severe consequences on river and coastal ecosystems. They lead to high nutrient levels that cause algal blooms, depleting oxygen in rivers and negatively impacting fish populations and other species.

Natural Resources Wales, the water company’s regulator, has been aware of the issues at the Cardigan plant for eight years but has issued no fines, only enforcement notices. Environmental campaigners argue that more action is needed. The regulator states that the issue is unresolvable without significant investment and infrastructure upgrades by Dŵr Cymru Welsh Water, which is the kind of investment that the public expects.

The Cardigan plant’s problems are closely tied to the use of a membrane to filter sewage, an unusual system installed in 2004. Saltwater intrusion into the system causes bacterial activity that leads to membrane blockages, backing up the sewage treatment process. Welsh Water plans to invest £20 million (approximately €23 million) at the site in 2025 to ensure full compliance with discharge permits.