About the data
How RiverFish works
A plain-English guide to where the records come from, what they mean and how to use them.
Where the records come from
RiverFish uses the Environment Agency’s National Fish Populations Database, a national collection of freshwater fish surveys in England. Survey identifiers, dates, locations and species names are retained so the evidence on each page can be traced back to the source dataset.
How waterways are assembled
The source groups survey sites under parent labels. RiverFish keeps those groups separate unless shared waterbody references, names and nearby coordinates give strong evidence that they are parts of the same waterway. This reduces the risk of joining unrelated rivers that happen to share a name.
Which pages can be indexed
All source groups can remain available as data pages, but not every label describes one real-world waterway. Survey projects, site collections, catchments and mixed tributary groups are excluded from search-engine sitemaps and marked noindex. Named rivers, brooks, canals and other coherent waterways remain browsable.
How fish names are counted
The source includes life stages, varieties, hybrids and broad groups as well as named species. RiverFish combines life-stage variations under the familiar species name and leaves uncertain or overly broad labels out of the headline total.
When a fish gets a detailed page
A river and species combination gets a detailed page when the data contains a valid length measurement and the fish was recorded at three or more sites or on five or more survey visits. Every valid individual length and weight is retained, with the sample size shown beside its summary. Combined bulk weights are kept separate and are not presented as individual fish weights.
What “recorded” means
A fish is “recorded” when surveyors observed or caught it during a survey. It tells you the species was found there at that time, not that it is easy to catch or still present today.
Why we don’t rank rivers
Survey methods and effort differ between places and years. That makes the records useful for discovering what has been found, but not for ranking fishing quality or showing population trends.
Targeted surveys
Some surveys look for a particular fish rather than the whole fish community. RiverFish keeps these records and labels recent targeted surveys clearly.
Map locations and access
Map points are rounded to protect precise survey locations. They show where surveys took place, not where fishing is permitted. Always check local access and fishing rules.
Live conditions and data dates
The fish records use the Environment Agency source snapshot dated 10 August 2026. Each waterway page shows its latest fish survey year. Live river levels and flow, where available, come from a separate Environment Agency monitoring feed and do not change the historical fish evidence. View the latest pipeline diagnostics.