Pollution – The biggest problem facing our freshwater environment

For one of my first field visits for WWF, I visited the Hogsmill, a much loved chalk stream in South London. I was shocked to see evidence of raw sewage and rags entering a river that is so vitally important for wildlife and recreation within the local community.

The Hogsmill Riverside Open Space, an area much enjoyed by children and dog walkers alike, is also home to Ewell Storm Tanks. These storm tanks were added in the 1930s to increase the capacity of Hogsmill Sewage Treatment Works (STW) and were inherited by Thames Water from the local authority in the 1960s, with an operational discharge consent designed for ‘occasional use’. The tanks were to provide a relief mechanism to prevent back up of sewage through the network at times of exceptionally high rainfall and use. Although ‘occasional use’ is not defined, it is not expected to exceed a few times a year. But, when the South East Rivers Trust carried out testing in 2016, they found that there were 14 discharge events between January and May.

Last month the evidence was clear to see, even after a long period of dry weather, a path from the storm tanks down to the river had formed littered with wet wipes and sanitary products. And that is only the visible evidence. Water samples captured during a discharge event at the Ewell Storm Tanks showed elevated E. coli levels downstream of the outfall, highlighting the potential risk to human health as the river is used for recreational purposes, with children and dogs often entering the river.

An outflow drain filled with sewage rags entering the Hogsmill River (L). Rags caught in branches in the River (R).

But the Hogsmill sewer overflow is not a one off – there are thousands of these across the country in every water company area. With population growth, more and more concrete covering permeable surfaces, and rain washing straight off of roads, there is an increasing demand on the sewerage system. Therefore, it is likely that these sewer overflows will spill raw sewage into Britain’s rivers more frequently and with greater volume. This is likely to be further exacerbated by predicted climatic changes with increases in both the frequency and intensity of rainfall events.

That’s why Blueprint is calling on water companies and regulators to get a grip on sewer overflows and stop pollution of our waters. In the Blueprint for PR19, we are calling for:

  • Strategic long-term wastewater plans – these are essential to prepare for the future and should ensure sewerage and treatment systems are sufficient to prevent pollution in the context of population growth and climate change
  • Targeting zero pollution incidents – it is not enough to just reduce the number of major incidents, dealing with pollution for sewer overflows should be a top priority and we welcome an increase in monitoring to understand the impact sewer overflows are having
  • Dealing with emerging pollutants – pollutants must be dealt with at source by promoting less harmful alternatives and investing into innovative natural treatment solutions, such as wetlands
  • Sustainable Drainage Systems (SuDS) prioritised – SuDS should be prioritised within a company’s own drainage scheme and used to reduce peak flows in the sewerage system, avoiding the need to invest in large underground pipes and providing biodiversity and amenity for local communities.

Alice Moore
UK Freshwater Assistant, WWF