Croydon Climate Action members supported Freshwater Watch and we took part in both their surveys in 2025.
Freshwater Watch is a citizen science survey by Earthwatch - they hold the Great UK WaterBlitz twice a year in Spring and Autumn. Samples test for nitrate and phosphate levels. They may be essential nutrients for life but they are also major pollutants, high levels cause excessive algae and plant growth, depleting oxygen, choking off aquatic life and destroying water quality.
Croydon River Action is a Croydon Climate Action campaign. We will continue to monitor our local waterways in 2026 through WaterBlitz, campaigning for action, sharing our results with the community and with local policymakers.
The Friends of Parks groups are doing the hard graft of cleaning up and maintaining our green spaces and waterways.
The Rivers Trust
Croydon River Action in 2025 and into 2026
The River Wandle in Wandle Park
Pollution - Moderate, results are consistent between April and September.
April 2025 - Nitrate: 1.75, Phosphate: 0.2
Sep 2025 - Nitrate: 1.75, Phosphate: 0.2-0.3
The River Wandle is one of our rare UK chalk streams, rare waterways of which there are only around 200 in the world.
Wandle Park is upstream from the Beddington works, where the Thames Water sewage outflow is. It is also upstream of the area where the February 2025 diesel spill entered the river. So the Wandle Park stretch is not affected by these pollution sources.
Upstream of Wandle Park, the Wandle is fed by streams such as the Caterham Bourne, these are often ‘occasional rivers’ found in our chalk landscapes. These streams pick up pollution from agricultural fields, sewage overflows, and streets such as litter, diesel, and tyre microplastics.
Flood risk is increased when rainfall is high. Water from rivers and streams is forced into culverts. The Caterham Bourne last rose in 2024 after considerable rainfall. It also flowed in 2020, 2014, and 2001 - the increased frequency could be indicative of our changing climate of hotter, dryer summers and wetter, colder winters.
The River Wandle at Waddon Ponds
Pollution - Low, Phosphate levels are similar to Wandle Park but Nitrate levels far lower.
Sep 2025 - Nitrate: 0-0.1, Phosphate: 0.2-0.3
Waddon Ponds alongside Wandle Park is one of the few places in Croydon where the Wandle can be seen above ground level.
The ponds themselves are fed by springs occurring at the junction of sand and chalk beds with London gravel beds.
Norbury Brook - Wandle Tributary
Pollution - High, both Nitrate and Phosphate levels are high.
Sep 2025 - Nitrate: 4-6, Phosphate: 0.4-0.5
Norbury Brook is a tributary of the River Wandle, it rises near Lower Addiscombe Road and flows north-west through Selhurst, Thornton Heath, and Norbury before joining the Wandle in south Wimbledon.
South Norwood Country Park - Chaffinch Brook
Pollution - High, both Phosphate and Nitrate levels were high in South Norwood Country Park.
April 2025 - Nitrate: 7-10, Phosphate: >1
When testing in the park the stream was dirty and smelly. The probable cause is pollution from misconnected sewage outlets.
