River Ching: Uncovering a Hidden Ecosystem in Northeast London

In a single day of sampling, we revealed more about the River Ching’s biodiversity than years of traditional surveying had managed, and demonstrated eDNA’s ability to uncover the hidden impacts of urban pollution.

The Client

The Ching Action Group is a team of local volunteers and citizen scientists who have spent three years monitoring pollution along the River Ching; a stream system running through Northeast London. Their chemical monitoring had successfully identified pollution hotspots, but the wider ecological impact of those hotspots remained a mystery. With funding from Thames21, they wanted answers. And a way to bring their local community along for the journey.

The Problem

The group faced two challenges. First, they needed a biodiversity baseline for the river, to understand how pollution and physical barriers like weirs were shaping species assemblages across different reaches. Second, they were struggling to engage the local community and needed something that could make people care about what was living beneath the surface of their local river.

“We’re hoping the eDNA data, when combined with our wider data pool, will evidence the need for change and guide our future restoration efforts,” said Natasha Furlong, Co-lead of the Ching Action Group. “We’re also hoping to repeat the surveys in a few years to hopefully demonstrate big improvements.”

Our Solution

Traditional biodiversity surveying is slow, disruptive, and narrow in scope. Each method targets specific species groups, meaning building a complete picture requires multiple separate surveys. eDNA changes that. By extracting and analysing environmental DNA from water samples, a single survey can simultaneously detect fish, invertebrates, plants, mammals, amphibians, and microorganisms across an entire river system.

We worked with the Ching Action Group to collect 12 eDNA water samples across 6 sites along the river. In our labs, we used 13 genetic markers and processed data from 33 different taxonomic groups, building a comprehensive biodiversity profile of the entire river in one visit.

Natasha noted the sampling was “similar to other water sampling we had done but much easier and less time consuming than other biodiversity surveying techniques. Less invasive and disruptive than other survey methods too.”

What We Found

The results revealed 1885 unique taxa across the sampling sites, including 929 microorganisms, 483 invertebrates, 298 plants, 41 birds, 30 mammals, 24 fish, and 6 amphibians. We also found 49 invasive species and 4 IUCN Red-Listed species, including the critically endangered European Eel.

The data told a clear story about the river’s health. Upstream sites showed strong signals of pollution-sensitive species, including newts, stoneflies, and clean-water fungi, which typically suggest good water quality. Immediately below a known sewage misconnection point, those species gave way to drain flies and pollution midges; pollution-tolerant insects that survive well near sewage effluent and contaminated waters. Further downstream, below multiple known pollution inputs, we found accumulations of Tubifex worms; an organism that thrives in heavily polluted organic sediment.

Fish species distribution provided a striking illustration of how barriers, such as weirs, fragment river ecosystems. Several species appeared only below a known barrier, as they are unable to move upstream.

Perhaps most valuably, the eDNA data flagged problems nobody had anticipated. The detection of out-of-place species like red deer and tuna pointed to urban contamination sources, while the distribution pattern of deer signals suggested an unidentified pollution outfall. “The main surprise was the red deer and Chinese water deer since they both start below the known polluting outfall and the scores get higher as they travel further down,” said Natasha, “so there’s likely another pollution source that we haven’t yet identified.”

“The results provided valuable insight into the different species assemblages across the river and supported our existing data, confirming our suspicions regarding the impact of weirs, misconnections, and high footfall.” Natasha added, “All of this will hopefully be useful data for supporting future funding bids and project proposals to deliver improvements.”

See the full report and dataset here.

The Impact

The efficiency gains were significant. The Ching Action Group’s existing Riverfly sampling covers just 3 sites, takes around 5 hours, records only certain invertebrate groups, and doesn’t reach species-level identification. By comparison, the eDNA survey covered 6 sites in a single day, identified over 100 invertebrate species, and simultaneously captured data on plants, mammals, amphibians, and more – groups that would otherwise each require their own targeted survey programme.

Beyond this, the results became a powerful community engagement tool. Presented at a local engagement event (see poster below), the findings sparked genuine curiosity and conversation, giving residents a new understanding of the wildlife living in their local river and a reason to care about its future.

The group plan to repeat the surveys in coming years to track improvements as restoration efforts take effect, building a long-term evidence base to support funding bids and demonstrate measurable change.