Frequently asked questions:
What are the key challenges the River Mole faces?
The Mole faces many challenges. It is a "flashy" river, with river levels rising and falling rapidly in response to rain. In winter in places it is prone to flood, in summer many tributaries become mere trickles and in extreme drought (e.g. 2022) the main river can run dry for several miles. Eleven Thames Water sewage treatment works discharge into the Mole and tributaries, contributing a substantial proportion of the total flow particularly in summer. Storm overflows discharged untreated sewage for a total of 13,000 hours in 2024. Summer conditions are particularly stressful for wildlife with high concentrations of pollutants and high water temperatures. There is a large and growing population with housing developments adding load on water supply and wastewater infrastructure. The river flows under and around Gatwick Airport. The M25 runs across the catchment with the runoff from this and other major roads adding pollutant load on the river system. Domestic misconnections are a particular problem for smaller tributaries. Much of the catchment is rural with agriculture contributing pollution from legacy phosphate, chemicals, animal sewage and soil loss. Invasive species including floating pennywort, himalayan balsam, american mink, and red-signal crayfish are widespread. Climate change increases the stressors and also highlights the importance of the river as a natural corridor for wildlife.
What could turn it round?
This could be a very long list! So here goes... Improving our wastewater treatment system - proper maintenance of existing facilities, investment to increase capacity and capability of these - more stringent discharge limits than today, tertiary treatment. Discharge Permits need to be set for to ensure environmental health in summer. Proper treatment of road runoff. Nature based solutions such as reedbeds to treat effluent from sewage treatment works. Well-designed sustainable drainage systems in all new developments. Wider deployment of catchment sensitive farming practices. Natural flood management. River restoration projects - re-meandering, gravel reseeding, removing barriers to fish passage, removal of invasive species. And this not address all the issues - e.g. pet insecticides, misconnections, etc., etc. It is a huge task which will take many years and substantial investment but it must be done for future generations human, aquatic and those that live around the river.
What are the issues?
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Water companies, including Thames Water, have not invested in upgrading the sewage works and infrastructure to cope with increasing population and extreme rainfall events.
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Environment Agency has not monitored or enforced any breaches of water standard regulations
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Farm runoff which contains silts and fertilisers, (phosphates and nitrates) causing too many nutrients in the river leading to algae growth. Silts coat the gravels making it harder for many river invertebrates to attach to the rocks and stones reducing their numbers. Historic levels of phosphates leach from soils into the river system.
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Road runoff which occurs when pollutants that settle on the surface of the road - such as residue from oil spills, as well as tyre and brake wear from vehicles - build up during dry weather and are then washed into rivers and streams when it rains. Toxic metals, hydrocarbons found in fuel and other pollutants washed into water pose a significant threat to river health. Road run-off can carry over 300 pollutants, causing short and long-term damage including killing fish and even discolouring water turning the river water black. https://www.london.gov.uk/press-releases/mayoral/study-shows-road-pollution-is-polluting-rivers
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Misconnections from domestic appliances which contain detergents and phosphates goes straight into tributaries, brooks and the river.
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Badly maintained septic tanks from properties that are not connected to the mains drains can leak untreated sewage straight into the the ground and water courses.
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Impact of pet flea treatments which contain nerve agents, Fipronil and imidacloprid. Parasiticides are commonly applied as ‘spot-on’ treatments on dogs and cats to prevent or kill fleas or ticks, but they contain toxic chemicals that are making it into UK rivers and ponds, particularly in urban areas. Many of these parasiticides contain a chemical in a class called neonicotinoids. These chemicals have been banned for agricultural use on crops as evidence shows they impact bees and other pollinating insects important for our food supply. https://www.imperial.ac.uk/news/243875/toxic-flea-tick-treatments-polluting-uk/
What is eutrophication?
This is when there is too much nutrient in rivers, lakes, reservoirs, estuaries or the sea, causing excessive growth of algae and plants. This adversely affects the quality of the water and our uses of it, as well as damaging the local ecology.
What causes eutrophication?
High levels of phosphates and nitrates.
What is the impact?
For more than two decades, the Environment Agency and other interested groups have identified the risks and impacts of freshwater eutrophication in England as a significant concern. Eutrophication increases the cost of drinking water abstraction and treatment, adversely affects angling, water sports and other recreational activities, and causes the loss of sensitive plants and animals in rivers and lakes.
What are the sources?
The main sources of phosphorus (P) in rivers and lakes are sewage effluent (primarily from water industry sewage treatment works) and losses from agricultural land . Food waste, food and drink additives and P dosing of drinking waters all contribute to sewage P loadings. Septic tanks and package sewage treatment plants are small sources nationally but can be important locally, particularly in the headwaters of catchments. Leaking water mains are a newly identified P source entering ground and surface waters .
Extracts from the Environment Agency publication 'Phosphorus and freshwater eutrophication: challenges for the water environment' December 2022
https://www.gov.uk/government/publications/phosphorus-challenges-for-the-water-environment