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Bug Hunting

The Anglers Monitoring Initiative: NorthEast Thames Area

Project Background

The Riverfly Partnership formed the Anglers Monitoring Initiative to address concerns amongst the fly-fishing, entomological and conservation communities that riverfly populations were in a national decline. The monitoring initiative, launched at the Riverfly Partnership Conference in May 2007, has enabled anglers to monitor the health of their local rivers and contribute to research on the decline of riverfly populations.

A series of successful workshops run by the Environment Agency and the Riverfly Partnership were set up in order to train the volunteers to be able to collect a three-minute kick sample and identify eight groups of river flies. These macroinvertebrates include the cased and caseless larvae of caddisflies, stonefly nymphs, four groups of mayfly nymphs and freshwater shrimp. 

Macroinvertebrates are ideal indicators of the biological quality of rivers as they have long life cycles and a limited mobility. This means that they are present throughout the year and can be easily sampled. The riverfly groups usually show a clear response to declining water quality as they are sensitive to organic pollution and insecticides. Freshwater shrimp are useful indicators in this angling initiative as they are also very sensitive to insecticide pollution, and are familiar to anglers who use a number of artificial fly patterns to represent them.

Kick Sampling on the Mimram

The Environment Agency monitors macroinvertebrates in both the spring and autumn on many of our rivers. However this frequency of monitoring may not detect pollution events that occur in-between sampling.  Monthly monitoring carried out by the anglers, as part of the monitoring initiative will check the biological quality more frequently and enable any gaps in monitoring to be filled.

The Riverfly Partnership uses the eight groups of river flies to form the Anglers Monitoring Index (AMI). The AMI is a very simplified index which uses the abundance category for each of the groups of macroinvertebrates to give a value. Abundance category A has a value of 1 and abundance category B has a value of 2 etc. These values are then added up to give a total score which is then compared to a trigger level.

Sample Sorting

Trigger levels are set using a baseline set of data collected over a period of about 6 months. Trigger levels should be set at a point below the normal level when the river is healthy but above the level that would be present if a pollution had occurred. This is hard to set on a river where little or no pollution data has been recorded and so in these cases historical data along with predictions (using a model) should be used.

If the data falls below the agreed trigger level (indicating that the water quality has fallen) then the anglers alert the Environment Agency who can investigate further.

River Mimram

Several members of Tewin angling club attended a flylife workshop in July 2008. The Environment Agency (in partnership with the Riverfly Partnership) funded their monitoring equipment.  Following their training two monitoring sites were registered – one main site to be sampled every month and one secondary site to be sampled every two to three months where time and resources are available.

Monitoring began in July 2008 (coordinated by Chris Mungovan). So far the monthly data has contributed to forming a seasonal baseline dataset from which changes in biological water quality can be easily detected and trigger levels can be set. Data is recorded and shared with the Environment Agency so that we can provide advice and a high level response if needed.


The graph above shows data from February 2010 to date and indicates scores tend to drop slightly around autumn. The trigger level has so far been set at 7 but this can be altered if any seasonal variation in scores becomes evident.

Biological quality of a river is classified under the Water Framework Directive (WFD) and the Mimram is separated into 3 different waterbodies under the directive: Mimram (Tributary below Kimpton) waterbody ID GB106038033370, Mimram (St Pauls Walden to Welwyn) waterbody ID GB106038033460 and Mimram (Welwyn to confluence with the Lee) waterbody ID GB106038033270.  The WFD status for waterbody GB106038033460 for macroinvertebrates is ‘High’ which indicates excellent quality. This means that the invertebrate community is diverse with a wide range of taxa and many pollution sensitive families are present. However, the WFD status for waterbody GB106038033270 is ‘Moderate’, which in terms of the WFD means improvements need to be made in order to achieve ‘Good’ status for macro-invertebrates, a requirement of the WFD. Currently the waterbody GB106038033270 is not classified for macroinvertebrates (for further information on the Water Framework Directive and how this relates to the river Mimram visit the Environment Agency website).

Monitoring for the anglers initiative usually takes place between April and September but this is purely optional. The Tewin anglers continue to sample into the winter months.

 The workshop has enabled the anglers to become competent in sample collection and identification and so little follow up advice has been needed. Any identification queries following the training have been answered via email.

Suspected Heptageniidae nymph (left) and Leuctridae Stonefly confirmation (right)

A photo of a suspected Heptageniidae mayfly was emailed for confirmation and quickly re-identified as a Leptophlebiidae mayfly. The correct identification of the stonefly family Leuctridae was also confirmed over email. Historic data was sent on request to Tewin angling club so that they could look at families recorded at one of our near-by routine monitoring sites along the River Mimram so that they knew what to look out for in the future.

Nina Lyman

Environmental Monitoring Officer

North East Thames Area

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