England Catchment Data Explorer · Cycle 3 (2019)
The headline figures
The reach spans two WFD water bodies: a heavily-modified river from Egham down to Teddington Weir, and the transitional (tidal) "Thames Middle" body below it. Neither is at "good", both fail on chemistry, and on both the Agency names sewage discharge among the reasons why.
Classification over time, 2009–2019
WFD status is reported in river-basin-management cycles. The grid below shows ecological and chemical status for both bodies at the three representative years. The ecological class has never moved — Poor on the river, Moderate on the tidal body — while chemical status flicked to Good in 2015 and back to Fail in 2019 on both bodies at once, a synchronised flip that points to a change in the standards, not the water (see "How to read this").
WFD status by cycle — both water bodies
Ecological and chemical class at 2009 (Cycle 1), 2015 (Cycle 2) and 2019 (Cycle 3, current)
GB106039023232 and GB530603911402
(/classifications.csv), pulled 2026-07-31. The 2015 → 2019 chemical
Good→Fail flip is a Cycle-3 standards change (ubiquitous PBDE / PFOS / mercury-in-biota), not a
measured local deterioration — see the caveats below. Provenance: RAW-PULL.
| Water body | Cycle (year) | Ecological | Chemical | Overall |
|---|---|---|---|---|
| River GB106039023232 | Cycle 1 (2009) | Poor | Fail | Poor |
| Cycle 2 (2015) | Poor | Good | Poor | |
| Cycle 3 (2019) — current | Poor | Fail | Poor | |
| Thames Middle GB530603911402 | Cycle 1 (2009) | Moderate | Fail | Moderate |
| Cycle 2 (2015) | Moderate | Good | Moderate | |
| Cycle 3 (2019) — current | Moderate | Fail | Moderate |
Interims (full matrix in wfd_status_full_timeseries.csv): a Cycle-2 2013
interim briefly scored the river Moderate overall; in the Cycle-3 2022 interim the
river's Invertebrates element improved Poor → High, but
Macrophytes & Phytobenthos stayed Poor, so the ecological class did not
move; chemical was recorded "does not require assessment" and the overall class was not re-issued.
RAW-PULL
Why it isn't "good": the EA's named reasons
For Cycle 3 the Agency publishes Reasons for Not Achieving Good (RNAGs) — each failing element tied to a business sector and activity. On both water bodies, "Waste water treatment — Sewage discharge (continuous)" is a named pressure (highlighted rows below), alongside agriculture, urban runoff and legacy chemicals.
River — Egham to Teddington (POOR)
| Element | Class | EA-named pressures (sector · activity) |
|---|---|---|
| Macrophytes & Phytobenthos | Poor | Water industry — sewage discharge (continuous); Agriculture — poor nutrient management → phosphate |
| Phosphate | Moderate | Sewage discharge (continuous); agriculture; urban transport drainage |
| Temperature | Moderate | Sewage discharge (continuous); impounded-water level management; low flow |
| Cypermethrin (priority) | Fail | Agriculture — poor pesticide management; Water industry — sewage discharge → chemical FAIL |
| PBDE, PFOS (priority substances) | Fail | Ubiquitous / legacy — "unknown, pending investigation" (see caveat: national artefact) |
| Heavily-modified designation | Mod. or less | Flood protection; drinking-water abstraction; navigation — target is "good ecological potential" |
Thames Middle — tidal (MODERATE)
| Element | Class | EA-named pressures (sector · activity) |
|---|---|---|
| Zinc | Moderate | Water industry — sewage discharge (continuous); urban development; contaminated bed sediments |
| Tributyltin (TBT) | Fail | Sewage discharge (continuous); landfill leaching; contaminated land; historic antifouling / restricted-substance use |
| Angiosperms / Saltmarsh | Moderate | Land-drainage structures (physical modification) |
| Dissolved Inorganic Nitrogen | Moderate | Supporting element (nutrient enrichment) |
| Mercury, PBDE, PFOS, PAHs* | Fail | Ubiquitous / legacy — "unknown, pending investigation" (see caveat: national artefact) |
| Hydromorphology | Mod. or less | Flood- and coast-protection use ("Hydrological Regime does not support good") |
*PAHs failing on the tidal body: benzo(g-h-i)perylene and benzo(b)fluoranthene. Chemical status is pass/fail on the worst substance, so a handful of ubiquitous compounds can carry the whole body to Fail. RAW-PULL
What the tidal "Moderate" is — and isn't
The tidal ecological Moderate is not a picture of dead biology. Under the estuarine classification tools, the living elements score well; the Moderate is driven by plants (angiosperms / saltmarsh), a supporting nutrient (nitrogen) and a specific pollutant (zinc).
| Element | Status | Element | Status |
|---|---|---|---|
| Fish | Good | Angiosperms | Moderate |
| Phytoplankton | Good | Saltmarsh | Moderate |
| Invertebrates | Good | Dissolved Inorganic Nitrogen | Moderate |
| Macroalgae | Good | Zinc (specific pollutant) | Moderate |
| Opportunistic macroalgae | High | Infaunal Quality Index | Good |
The "good" objective, relaxed to 2063
WFD lets the Agency set alternative objectives — a later deadline, or a lower target than "good" — where meeting good by the default date is judged technically infeasible or disproportionately costly. On this reach the chemical "good" objective has been pushed to 2063 on both bodies, and the ecological/overall objectives are set no higher than the current class. The reason codes matter for the accountability question, because they include "disproportionately expensive — disproportionate burdens".
| Water body | Item | Objective | Target year | EA reason codes (paraphrased) |
|---|---|---|---|---|
| River GB106039023232 | Chemical | Good | 2063 | Technically infeasible (no known solution); natural conditions — chemical recovery time; cause of impact unknown |
| River GB106039023232 | Ecological | Poor | 2015 | Technically infeasible (no known solution); practical technical constraints prevent earlier action |
| Thames Middle GB530603911402 | Chemical | Good | 2063 | Technically infeasible; disproportionate burdens; natural conditions — chemical recovery time |
| Thames Middle GB530603911402 | Ecological | Moderate | 2015 | Disproportionately expensive (unfavourable cost–benefit; disproportionate burdens); good status prevented by HMWB designated use |
Read plainly: on the tidal body the Agency has formally recorded that getting to good would be "disproportionately expensive" and impose "disproportionate burdens", and has moved the chemical deadline four decades out. That is the documentary backdrop to the fines-versus-investment debate — but it is a statement about cost/feasibility judgements, not proof of any single party's culpability. RAW-PULL
How to read this
Caveats a regulator would press — stated up front
- The chemical FAIL is largely a national artefact. The synchronised 2015 → 2019 Good→Fail flip on both bodies is driven by ubiquitous persistent, bioaccumulative toxicants — mercury-in-biota, PBDE and PFOS — newly added to the chemical standards in Cycle 3. These fail in almost every English water body, carry a documented "natural recovery time", and are not solely attributable to Thames Water. Do not read the chemical Fail as a local, present-day collapse. PUBLISHED context on the standards; RAW-PULL for the classification.
- Tidal biology is healthy. Under the estuarine tools, Fish, Phytoplankton, Invertebrates and Macroalgae all score Good/High on Thames Middle. The Moderate is chemistry (zinc), a plant/nutrient signal (angiosperms, saltmarsh, nitrogen) and hydromorphology — not dead biology. On the river, Invertebrates even improved Poor → High by the 2022 interim, though phytobenthos (the phosphate-sensitive element) held the ecological class at Poor. RAW-PULL
- Named pressure ≠ sole cause; correlation ≠ causation. A RNAG names sewage discharge as a pressure, but the same elements list agriculture, urban drainage and legacy contamination too. The classification identifies pressures; it does not apportion blame or prove that any one discharge caused any one failure. RAW-PULL
- Zinc — the tidal Moderate driver — is unmonitored in open data. Zinc has zero records at all 12 public water-quality points on the reach, so the Agency's own zinc classification cannot be corroborated from the open archive. A named cause we cannot independently check. PROVEN GAP
- Water-body codes on this reach do not line up. The tidal classification here is
GB530603911402(Thames Middle), but Mogden's sewage outfall and the tidal fish/benthic monitoring are codedGB530603911403— an adjacent body on the same reach. The sewage RNAGs cited above belong to…402; reconcile the codes before attributing a specific outfall to a specific classification. RAW-PULL - Attribution and interims are Cycle-3-only / partial. RNAG pressure-attribution is published for Cycle 3 only; 2022 was an interim update (chemical "does not require assessment"; overall class not re-issued), so year-on-year "trend" reading is limited. The river is also a heavily-modified water body — its ecological target is "good potential", not a pristine reference state. RAW-PULL
Sources & provenance
- RAW-PULL EA England Catchment Data Explorer —
https://environment.data.gov.uk/catchment-planning/WaterBody/{GB106039023232 | GB530603911402}with/classifications.csv,/rnags.csv,/objectives.csv. Downloaded 2026-07-31. - Working datasets:
/tmp/thames_datastore/wfd_status/—wfd_status_over_time.csv,wfd_status_full_timeseries.csv,wfd_rnags_cycle3.csv,wfd_key_elements_cycle3_2019.csv,wfd_objectives_targets.csv, plus the six raw per-body CSVs. - PROVEN GAP Zinc has zero observations across all 12 reach water-quality points (WIMS archive) — cross-referenced from the water-quality domain pull.
- PUBLISHED The Cycle-3 chemical-standards change (mercury-in-biota / PBDE / PFOS added, causing near-universal English chemical Fail) is a national methodology point, not a Thames-specific measurement.