Services · Specialist

Electrofishing Surveys

Electrofishing is the standard method for assessing freshwater fish populations. We deliver EA-consented surveys for development impact assessment, fish rescue and translocation, and pre- and post-construction monitoring.

SeasonJune – October
ConsentEA authorisation required
MethodsDepletion & semi-quantitative
ApplicationFish rescue / EIA / monitoring

Overview

Electrofishing uses a controlled electric current passed through the water to temporarily stun fish, allowing them to be netted, identified, measured and returned alive. It is the standard and most widely used method for assessing freshwater fish populations in UK rivers, streams and still waters, and is the only practical method for comprehensive fish community assessment in many habitats.

We hold Environment Agency consent for electrofishing operations and deliver both quantitative (depletion) and semi-quantitative surveys depending on the assessment purpose. Quantitative depletion surveys — three successive passes through a defined reach — provide robust population density estimates. Semi-quantitative surveys — a single timed catch per unit effort — are used for broader community characterisation and species presence/absence.

Common applications include baseline fish population assessment for Environmental Impact Assessment, fish rescue and translocation ahead of in-river works (dewatering, culverting, channel diversion), pre- and post-construction monitoring to detect impacts and monitoring of fish populations in rivers, lakes and ponds for conservation and fisheries management purposes.

When you need this

  • In-river works (culverting, dewatering, channel diversion) require fish to be rescued and relocated
  • An EIA requires baseline fish population data for a watercourse
  • Pre- and post-construction monitoring is conditioned by the LPA or Environment Agency
  • A new or modified water intake or discharge could affect fish populations
  • Fish population data is needed for river restoration or fisheries management

Our approach

  1. 01
    EA consent and planning

    We obtain Environment Agency authorisation for the electrofishing operation and plan the survey design — site selection, methodology, timing and health-and-safety risk assessment.

  2. 02
    Electrofishing operation

    A team of trained operatives uses bank-based or wading electrofishing equipment to pass a controlled current through the water. Stunned fish are netted immediately and transferred to holding tanks with aerated water.

  3. 03
    Processing

    All fish are identified to species, measured (fork length), weighed where appropriate and assessed for condition before being returned alive to the watercourse (or translocated to a receptor site for fish rescue operations).

  4. 04
    Analysis and reporting

    Population density estimates, community composition, size-class structure and condition data are analysed and reported with an assessment of the fish community status and recommendations for mitigation or monitoring.

Frequently asked questions

01Does electrofishing harm the fish?+
No — when carried out correctly by trained operatives using calibrated equipment, electrofishing temporarily stuns fish for a few seconds. They recover fully in the holding tank within minutes and are returned alive to the watercourse. The method is endorsed by the Environment Agency as the standard survey technique for freshwater fish.
02Do I need an Environment Agency consent?+
Yes. Electrofishing can only be carried out with prior written authorisation from the Environment Agency. We hold the necessary consents and handle the application process as part of the survey commission.
03What is a fish rescue?+
A fish rescue is an electrofishing operation carried out to remove fish from a section of watercourse before it is dewatered, culverted or otherwise made unsuitable. Captured fish are translocated to a suitable receptor site upstream or downstream. Fish rescue is a common condition for in-river construction works.
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