NRW Freshwater Fish Surveys
Natural Resources Wales
Freshwater fish are used as an indicator of stock status, water and habitat quality, artificial obstacles to migration and river flow requirements due to specific life-cycle requirements. This dataset is made up of the species count and length values from the freshwater river fish surveys conducted across Wales by Natural Resources Wales and former Environment Agency Wales. These surveys are conducted as part of on-going monitoring of fish in their natural environment for legislative requirements and to meet business drivers.
A strict methodology is applied when sampling for freshwater river fish. There is a core network of sites which are monitored on an annual basis, and also catchment-wide surveys on a six-year rolling programme. These sites are located in habitat types suitable for the respective fish species. In addition, sites may be sampled for investigative work, or on an ad hoc basis. Sampling areas are commonly 50 metres long and the full width of the river and may embrace different flow types and substrate. For CATCH PUE survey strategy the effort is based on a time measurement. Electric fishing is the most commonly used sampling method, although alternative methods are available for different strategies, such as netting and trapping. Once a sample of fish is collected, they are immediately identified in the field, measured and counted and then released alive into the same section of river from where they were captured.
For many of our surveys we record an NGR at the site because this acts as a central/representative location around which we collect lots of samples. An NGR is then also recorded against each of the samples to give a more accurate sampling location.
Redactions
Some information has be redacted to make the data openly available. This includes
Third party data
Data collected for ongoing investigations
Cancelled or incomplete surveys
Update Frequency
This data is continually update with the most surveys undertaken in the summer. Data from survey seasons is often not enter at the time of capture and can be several months before its is entered into the system. The external dataset is updated monthly to include new data, and may also contain corrections to previously published data due to quality assurance work.
Information Warnings
- Freshwater fish survey data is available from 1974 to present. A caveat being that historical data are sporadic until 2001. This is because fish survey data collected before 2001 were often saved in local databases and not the national ones (KiEco and formerly NFPD).
- Fish surveys are carried out by a range of survey methods, the data from one survey is not necessarily directly comparable to another. For example, the total fish count may be based on multiple or single run surveys or Catch Per Unit Effort (CPUE) surveys. The user is recommended to check the survey method used in the data provided.
- We do our best to avoid data quality problems, but as these datasets reflect the data we hold, they may contain errors
The data is provided a
Further Information:
Please see the following documents for further information: Further Information
The taxa data can also be viewed and downloaded from the NBN Atlas. Accessing the taxa data this way offers several advantages. It can be viewed alongside a wide range of taxa from other surveys conducted by various individuals and organizations. Furthermore, the taxa can be explored through its full taxonomic hierarchy via integration with the UK Species Inventory, which is the most comprehensive curated database of UK wildlife taxonomy and nomenclature.
Attribution statement
Contains Natural Resources Wales information © Natural Resources Wales and Database Right. All rights Reserved.
Use this data in another application
Please refer to the licence to understand the conditions of using this data.
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- Type:
- Spatial data
- Category:
- Environment
- Publication date:
- 19 August 2025
- Licence:
- Open Government Licence for Public Sector Information (OGL)
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Copyright:
- Point of contact:
- opendata@naturalresourceswales.gov.uk
- Language
- English