Catchment Catalyst

Click the map to select a river catchment, or enter a postcode

Eco Class Good Moderate Poor Bad

Catchment Ranking: 27/92

Catchment Ranking

The ranking is derived from the EA 2025 classification data. Parameter scores are normalised and an average is taken. Rankings are restricted to prevent e.g. a "moderate" river being ranked higher than a "poor" river.

(92 river waterbodies in the North Devon Catchment)

EA Ecological Classification

  • 2022Moderate
  • 2019Moderate
  • 2016Moderate

Failing Elements

  • Phosphate
  • Phytobenthos Sub Element

EA RNAGs

  • Poor nutrient management
  • Sewage discharge (continuous)

Mully Brook

Why is the river failing?

Mully Brook is currently at Moderate Ecological Status. The principal failing element is phytobenthos, with an EQR of 0.463, below the Good threshold of 0.60. Fish are achieving High status (EQR 0.88), invertebrates are High status, and physico-chemical indicators are High status except for phosphate at Moderate.
The Environment Agency has identified poor nutrient management and continuous sewage discharges as RNAGs. However, unlike many neighbouring water bodies, the phosphorus source evidence is dominated by wastewater. The detailed source model attributes approximately 84% of phosphorus loading to South West Water sewage treatment works, with livestock contributing only around 10%.
This makes Mully Brook one of the clearest wastewater-driven nutrient water bodies in the Mole catchment. The river retains strong biological status for fish and invertebrates, suggesting that significant ecological recovery may be achievable if phosphorus pressures are reduced.

What is happening now?

Current activity includes Northern Devon Natural Solutions, regulatory farm inspections, review of discharge permits, investigations to inform PR29 and delivery of Devon Woods.

Risk Levels

Risk Levels

  • SWW Overflows: Total duration of intermittent spills for all CSOs in the catchment for 2025.
  • Private Sewage: Density rating based upon non-SWW properties in the catchment.
  • Livestock: APHA data from Feb 2026.
  • Runoff: ESME modelling (wf_r24).
  • Modification: ESME modelling (aa_r1).
  • Invasive Species: ESME modelling (iv_r17).
  • Overheating: derived from tree cover ESME modelling (wq_r10).
  • Running Dry: Abstraction sustainability ESME modelling (ws_r27).
  • Untreated SewageVery High
  • ModificationMedium
  • Sewage (Private)Low
  • Invasive SpeciesLow
  • LivestockHigh
  • OverheatingLow
  • RunoffHigh
  • Running DryVery Low

Intervention hypothesis (confidence: High)

The evidence is unusually consistent. Both RNAGs are relevant, but wastewater clearly dominates the nutrient profile, accounting for the overwhelming majority of modelled phosphorus inputs. This is reflected in the current programme, which already includes regulatory review of discharges and investigations feeding into future investment planning.
The most plausible route to recovery is therefore reduction of continuous wastewater discharges. Agricultural measures remain appropriate as supporting interventions, but they are unlikely to deliver recovery on their own given the scale of the wastewater contribution.

Intervention Size of Intervention Estimated Cost Lead
PRIORITY INTERVENTIONS (NOT IN ORDER OF PRIORITY)
Investment in STWs (phosphate reduction) £3m SWW
Investment in storm overflows (reduction in spills) AMP9 £7m SWW
SECONDARY INTERVENTIONS
Riparian tree planting 2.2km (8.8km) £44,000 ND Biosphere Foundation

What needs to happen to bring each waterbody up to "Good" ecological status? Our Waterbody Dashboard integrates data on water quality, land-use, livestock, sewage and wastewater, river obstacles, pollution risks, and more to answer this fundamental question. Working with the catchment partnership, we've used the data to draw out the interventions required to improve water quality to "Good" for each river catchment.

The Waterbody Dashboard is best viewed on a laptop or PC, but can be viewed on a phone. Use the button at the bottom right to expand the dashboard to full screen.

Understanding the dashboard

Much of the data shown in the dashboard is publicly available, however it can be hard to find and even harder to understand. In bringing the data together, we have sought to display the most relevant information in a format that is easily understood by the general public. For the dashboards to be of most value and to build trust, we are keen to be transparent about where the data comes from and how we have created our ranking and scoring systems. We therefore provide below a full explanation for every visualisation shown on the dashboard.

Left-hand panel

Map of Catchments displays the sub-catchment as defined by the Environment Agency (EA) under the Water Framework Directive. Each sub-catchment is colour coded in line with the colours used by the EA on their Catchment Data Explorer. Our map displays the 2025 Ecological Classification. Note as at October 2026 the EA system does not yet show the 2025 data.

Catchment Ranking is calculated using the EA classification data. The latest EA score for each measured parameter, as shown on the EA Data page, has been standardised as individual scores between 0 and 1. An average of these scores is then taken. The ranking for a waterbody is constrained within its Ecological Classification; this prevents, for example, a "moderate" river being ranked higher than a "poor" river. A spreadsheet containing the data, the calculations, and detailed documentation is available upon request. "...\BIOSPHERE\PowerBI\Waterbody Scorecards\Source data\EA Standardised Scoring\EA Standardised Scoring.xlsx"

EA Ecological Classification displays the classification assigned over the last three assessment periods by the Environment Agency. This can be found on their Catchment Data Explorer.

Failing Elements data is taken from "WFD_River_Canal_and_SWT_Water_Bodies_Cycle_4_Classification_2025.xlsx" available for download here:
https://environment.data.gov.uk/dataset/0efd50a1-ce1a-4958-a414-198d32798204

EA RNAGs are the Reasons for Not Achieving Good ecological status, as defined by the EA. This data is taken from "Rivers Trust WFD_Reasons_for_Not_Achieving_Good_(Cycle_3).csv" available for download here: https://data.catchmentbasedapproach.org/maps/0b10befb9ec8456f924ae6eeda1df187

River Status

Why is the river failing? explains why the waterbody is not at "Good" ecological status. This summary draws upon the data in the dashboard, as well as local knowledge, and insights from partner organisations.

What is happening now? provides information on current projects and initiatives related to improving the health of the waterbody. Please contact us if you are aware of further work underway in this catchment.

Main pressure is a high level indicator of the main issue preventing "Good" status and provides a focus for the interventions required. The categories are: wastewater, agriculture, mix (of wastewater and agriculture), fish (where fish populations are poor), and special cases (for factors such as mining etc.) This assessment is based upon the phosphate source apportionment modelling (Land Use Data page), the EA RNAGs, and the other data shown across the dashboard.

Intervention hypothesis draws upon the reasons for failure and outlines the restorative action needed to bring the waterbody up to "Good" ecological status.

Intervention table lists specific interventions that should be progressed in order to restore river health. Most of these actions will require specific funding streams to be identified for the work to go ahead.

Risk Levels

We are keen to use the best models available for our risk scoring. If you are aware of a better model for any of our risk scoring, please let us know.

  • SWW Treated Sewage is calculated using the Source of Phosphate 2025 data on the Sewerage Data page, and the Latest Phosphate value from the EA Data page. The calculation is (Source of Phosphate 2025 / 100) * Latest Phosphate. The score is then translated to a rating as follows: < 0.005 = Very Low, 0.005 - 0.01 = Low, 0.01 - 0.02 = Medium, 0.02 - 0.03 = High, > 0.03 = Very High

  • SWW Overflows is based upon the 2025 spills data from South West Water. The total hours of spills for all storm overflows in the catchment are added together. Very Low < 5 days, Low 5-10 days, Medium 10-30 days, High 30-60 days, Very High >60 days

  • Private Sewage is based upon the number of properties in the catchment not on mains sewerage (see Sewerage page). A density rating is calculated by dividing the number of properties on private sewerage by the catchment area to get "private sewerage per ha". The score is then translated to a rating as follows: Very Low <0.10, Low 0.10-0.15, Medium 0.15-0.30, High 0.30-1.00, Very High >1.00

  • Invasive Species is based upon data from the Environmental Agency's Ecosystem Service Map Explorer (ESME). The explorer can be viewed here: NEW: Ecosystem Service Map Explorer | Water Data Explorer | Engage Environment Agency The invasive species modelling is described in section R17 (pg.92) of Riverine Natural Capital Condition and Ecosystem Service Mapping Project: methodology report For river waterbodies, the indicator is scored as “No species present” or “Species present”. “Species present” means that at least one INNS was recorded within the river water body. For our pressure score, we have assigned "No species present" as "Low" and "Species present" as "High". This risk score is crude and local intelligence will provide more valuable insights.

  • Run-off is based upon data from the Environmental Agency's Ecosystem Service Map Explorer (ESME). The explorer can be viewed here: NEW: Ecosystem Service Map Explorer | Water Data Explorer | Engage Environment Agency The run-off modelling is described in section R24 (pg.107) of Riverine Natural Capital Condition and Ecosystem Service Mapping Project: methodology report The scoring combines Manning’s roughness coefficients for major habitat types with BGS Hydrogeology mapping to produce a 1 to 5 output. For our pressure score, we have assigned 1 = Very High, 2 = High, 3 = Medium, 4 = Low, & 5 = Very Low

  • Livestock is based upon head counts of poultry, beef cattle, dairy cattle, pig, & sheep from the Animal and Plant Health Agency (APHA). The data was sourced via a Freedom of Information Request in Feb 2026. Data will be refreshed at least annually. Headcounts were converted to expected Nitrogen and Phosphate emissions for the different livestock:

    • Nitrogen Load assumes the following kg N/yr per head: Beef 70, Dairy 110, Pig 20, Poultry 0.7, Sheep 13
    • Phosphate Load assumes the following kg P/yr per head: Beef 13, Dairy 23, Pig 5, Poultry 0.3, Sheep 5

    The resulting data was summed, and then divided by the catchment area to provide a density rating of N+P load per year in kg per SqKm. For our pressure score, we have assigned > 40,000 = "Very High", 20,000-40,000 = "High", 10,000-20,000 = "Medium", 5,000-10,000 = "Low", <5,000 = "Very Low"

  • Running Dry is based upon data from the Environmental Agency's Ecosystem Service Map Explorer (ESME). The explorer can be viewed here: NEW: Ecosystem Service Map Explorer | Water Data Explorer | Engage Environment Agency The abstraction sustainability modelling has been used, see section R27 (pg.76) of Riverine Natural Capital Condition and Ecosystem Service Mapping Project: methodology report The scoring combines Environment Agency WRGIS Abstraction Licensing Strategy and WFD Cycle 2 Hydrology of Flow Compliance data, to produce a 1 to 5 output where 5 indicates the waterbody can support sustainable extraction of water. We have inverted this scoring for our Running Dry risk score, so that 5 = Very Low, 4 = Low, 3 = Medium, 2 = High, 1 = Very High. The ESME abstraction score is not ideal for this pressure score and we would welcome other suggestions.

  • Overheating is based upon data from the Environmental Agency's Ecosystem Service Map Explorer (ESME). The explorer can be viewed here: NEW: Ecosystem Service Map Explorer | Water Data Explorer | Engage Environment Agency The River Shade modelling has been used, see section R10 (pg.60) of Riverine Natural Capital Condition and Ecosystem Service Mapping Project: methodology report The scoring uses the Environment Agency’s Keeping Rivers Cool dataset and outputs a score of No Shade, Medium Shade, or Shaded. For our Overheating pressure score we have assigned No Shade = High, Medium Shade = Medium, Shaded = Low.

  • Modification is based upon data from the Environmental Agency's Ecosystem Service Map Explorer (ESME). The explorer can be viewed here: NEW: Ecosystem Service Map Explorer | Water Data Explorer | Engage Environment Agency The River Habitat Quality modelling has been used, see section R1 (pg.52) of Riverine Natural Capital Condition and Ecosystem Service Mapping Project: methodology report The scoring uses River Habitat Survey (RHS) data and combines data from site assessments with modelled data where there are gaps. The output is a score of 1 to 5 where 5 indicates a high degree of naturalness. For our Modification pressure score we have inverted the scores so that 5 = Very Low, 4 = Low, 3 = Medium, 2 = High, 1 = Very High

EA Data

The Environment Agency (EA) Scoring table is driven by publicly accessible Water Framework Directive (WFD) data downloadable from the EA website, plus detailed scoring data obtained via a Freedom of Information Request in April 2026. One of the overriding aims of the Catchment Catalyst Dashboard is to understand how "close" each waterbody is to "Good" ecological status. In order to quantify this, we need the actual scores for each of the parameters surveyed by the EA. This table presents the EA scoring data for the last 4 cycles.

The table cells are colour coded in line with the colours used by the EA on the Catchment Data Explorer. Grey cells indicate there is no data for this parameter. The table is divided into the sections that contribute to the overall Ecological classification. Ecological shows the overall classification for each of the classification years. The Biological section provides the scoring data for Fish, Invertebrates, Plants and Algae. If any of these are rated as Bad or Poor, the overall classification will also be rated as Bad or Poor. The Physico-chemical section provides the measurements for key water quality properties. Note that a Bad or Poor measurement will NOT decrease the overall ecological classification to Bad or Poor (only the Biological elements can do this). The Hydromorphological section provides the assessment of how "natural" the river is. This rating can only be at High or Not High. For detailed information on how waterbodies are classified under WFD, visit https://www.wfduk.org/ and search for this report published in 2022 "Rules for assessing surface water body ecological status and potential"

The expected levels of physical-chemical properties, fish, invertebrate, and plant communities, varies between different types of rivers. Fast-flowing, upland rivers are very different environments to wide, slow flowing lowland rivers. To account for this variance, different thresholds are assigned for different waterbodies. These thresholds can be seen on the right of the table. Note thresholds can change over time, and the dashboard shows the most recent thresholds.

Note that exceptions apply for some waterbodies. For example, in North Devon, Coney Gut and Taw Estuary are Heavily Modified and therefore their ecological class is held at Moderate even though Biology is rated "Poor" and "Bad" respectively. Venn is reduced to Moderate due to failing on Specific Pollutants. A banner at the bottom of the table indicates these exceptions.

Data sources:
WFD River, Canal, and SWT Water Bodies Cycle 4 Classification 2025 (Full Resolution) Defra Data Services Platform
The Freedom of Information Request EA scoring data is available upon request, please email biosphere-mailbox@devon.gov.uk

Land Use Data
Sewerage Data
EA Inspection Data