River Chess Association

Our riverfly monitoring team have discovered a decline in the invertebrate populations in a Chesham stretch of the river. During our routine surveys in August, the population recorded at the Broadwater Bridge site (by the Latimer Road) was low enough to breach a "trigger level" set by the Environment Agency (EA). This could mean that something is amiss with the river in this area, as a good, balanced invertebrate population is an indicator that the river is healthy. After double-checking our results, we reported our concerns to the EA.

A survey by an EA Monitoring Officer confirmed our data and further investigations were carried out to identify the cause. The good news is that major water quality problems (such as a pollution incident) have been ruled out. However, EA data suggest that the diversity of invertebrates has been declining at this site over the last decade, with the loss of insects from groups such as Ephemeridae (mayflies) and Glossosomatidae (caddis flies).

The EA's current conclusion is that the invertebrate population is suffering as a result of low flows and habitat problems. Siltation, caused by urbanisation increasing the amount of  rainwater run-off from roads entering the channel, may also be an issue. The EA is investigating these issues as part of the EU Water Framework Directive and our monthly data are contributing to their research.

Meanwhile, we continue to survey our seven study sites along the Chess, helping to build up a picture of long-term trends in the population, as well as monitoring for pollution events. You might spot us from time to time out on the river in our hi-vis jackets! To find out more about this element of our work, please see out riverfly monitoring page. 

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