Sources

Where the data come from and how they can be used.

The map has two views: reports and metrics.

The Dated reports view uses exported files. Water & weather metrics and the history charts read the database. Both show observation dates. Reloading the page reads the data we already have; it does not collect new measurements.

Metrics and colours

Choose Water & weather metrics, select a source, then use Colour by metric. Each station shows the latest measurement we have. After moving the map, choose Search this view. A search returns up to 1,000 metrics and tells you if more are available.

Colours compare measurements with the same definition, unit, method, sampling period and height reference. Gauges with different local zeros use separate scales. Colours show the range of values, not safety levels; values between stations are unknown. You can filter by age. Bounds and invalid values stay in the history but are excluded from colours; flagged readings appear dimmer.

Tidal measurements with a common height reference are labelled Latest archived tidal level. Those without a supplied reference say Latest archived tidal reading. Collection is daily, so neither is a live tide level or prediction. These station measurements do not show flood extent.

Dates

The observation date is when a measurement was taken or a status recorded. The retrieval date is when we obtained it; the export date is when we prepared the map file. These dates can differ, especially for laboratory results and older records.

A measurement records a variable at a particular time. A metric is a set of measurements. The popup fits each metric’s chart to its available dates; Shared period aligns the charts. Past year covers the previous 365 complete UTC days. Gaps may reflect infrequent sampling, missing source data or unfinished imports.

Dated export evidence: monitoring observations, overflow status and bathing water. The interactive map reads retained records through the API. Map geometry sources and the API guide explain coverage and source identifiers.

Environment Agency

Missing units in the dated Hydrology summaries are resolved using the publisher's series definitions and checked measure identifiers. Each recovered unit retains its evidence link; observation values and dates stay unchanged. Oxygen concentration and percentage, and the different conductivity units, remain separate. See the unit definitions.

River and groundwater levels, flow and rainfall come from the Environment Agency's Flood Monitoring and Hydrology services. Laboratory water-quality results come from the Water Quality Explorer; bathing-water observations come from the Bathing Water Quality service.

Contains Environment Agency information © Environment Agency and/or database right. Licensed under the Open Government Licence v3.0. Records are selected and reformatted for this service.

History views include explanations and references where we have checked them. Units, sample type and qualifiers such as “less than” are part of the measurement.

Thames Water

Current-status map layer: Thames Water Storm Overflow Activity © Thames Water, licensed under CC BY 4.0. The layer is filtered and reformatted for this map, and status codes are expanded into readable labels. The publisher's dataset metadata identify this licence.

Dated alert history: Thames Water Open Data © Thames Water. Dated storm-overflow alerts are filtered and reformatted for this service. Reuse is subject to the separate Thames Water Open Data Terms of Service. Its 2024/25 Open Data Rationale describes an attribution-based open-data licence. The ArcGIS layer's CC BY licence is not assigned to this separate feed.

An overflow activity indication does not measure the volume released, pollutant concentration or conditions at a swimming location. A dated status point is not automatically a discharge interval. Read the publisher's storm discharge and flow guidance alongside these observations.

Defra UK-AIR

Station observations are obtained from the UK-AIR data archive. © Crown copyright 2021 Defra via uk-air.defra.gov.uk, licensed under the Open Government Licence, following the publisher's licence and attribution notice.

The copyright notice's year is separate from the observation dates. Records are selected and reformatted, with source units and verification information retained where supplied.

Met Office

Met Office UK Land Surface Observations: British Crown copyright 2024–2025, the Met Office, licensed under CC BY-SA 4.0. Selected records are reformatted for the database and charts; retrieval dates accompany the records.

Adapted Met Office data supplied by this service are made available under CC BY-SA 4.0. This notice applies to that material. Other feeds retain their own reuse terms.

Map data

London borough boundaries: Source: Office for National Statistics licensed under the Open Government Licence v.3.0. Contains OS data © Crown copyright and database right 2025. The map uses the London subset of the December 2025 Local Authority District boundaries. See the ONS geographical licence notice.

River lines: Contains OS data © Crown copyright and database right 2026. OS Open Rivers, April 2026 release, under the Open Government Licence v3.0. Geometry is transformed, clipped and simplified for display. Small streams and underground rivers may be missing.

Background tiles: © OpenStreetMap contributors. OpenStreetMap's data licence and the separate tile usage policy apply. Attribution also appears on the map itself.

The 50 km circle around London is a collection and display area. It is not a river catchment boundary. The source dates and processing details are retained in the geometry metadata.

Earthquakes and fires

Earthquakes: U.S. Geological Survey, through its earthquake catalogue service. Source and event identifiers are retained. USGS-produced data are in the US public domain; the agency requests credit, and separately credited third-party material can have different terms. See USGS copyrights and credits.

Active-fire detections: NASA FIRMS / NASA LANCE, part of NASA's Earth Science Data and Information System (ESDIS). The configured satellite product is VIIRS NOAA-21 near-real-time active-fire detections. Records are selected and reformatted; satellite and product identifiers remain with the data. NASA FIRMS provides reuse and citation guidance, including acknowledgements for scientific publications.

These feeds provide wider context where available. A satellite active-fire detection is not a surveyed fire perimeter or a measurement of burned area.

Reuse

Keep the provider, original identifier, measurement date, units, qualifiers and source credit with exported records. Follow the terms linked for each source and identify changes you make. Publication here does not imply endorsement by the data providers.

Credits and source notices checked on 24 September 2026. Observation dates are shown with the data.