When you gaze curiously into the depths of a river you might spot fish or water plants, but if the habitat is healthy there is often much more life to be found hidden beneath the surface. Some insects spend months or years underwater during their larval stages, the most well-known being dragonflies and mayflies.

Riverflies are very sensitive to surrounding conditions, which means tracking their abundance gives a good indication of the health of a waterway. CRT volunteers Giles Adams and Jenny Ashdown are helping to monitor the condition of the River Stour where it flows through Bere Marsh Farm in Dorset, by counting the number of riverflies in the water.

They are carrying out surveys once a month during the summer, and their findings are sent to the Anglers’ Riverfly Monitoring Initiative (ARMI). This scheme was introduced by the Riverfly Partnership in 2004, to supplement the Environment Agency’s monitoring so that water quality is checked more widely and action is taken if concerning changes are detected.

Giles and Jenny have taken part in the Riverfly Partnership’s training, which means they can now carry out the standardised kick sampling method required by the programme.

The 'canaries' of our rivers

Canaries were once taken down into mines as they are sensitive to toxic gases that can build up underground and would react to them more quickly than the people working. Riverflies are known as the 'canaries' of rivers as they are sensitive to agricultural run-off high in nutrients, pollution from sewage discharges and many other factors, so monitoring them gives us a picture of a river’s health. Thankfully they aren’t harmed during the process, unlike the unfortunate canaries.

The scheme focuses on three key groups of riverflies: up-winged flies or mayflies (Ephemeroptera), caddisflies or sedges (Trichoptera) and stoneflies (Plecoptera). More than 270 species of these have been recorded in the UK, but the study monitors eight types – cased caddis (below), caseless caddis, mayfly, blue-winged olive, flat-bodied upwing, olive, stonefly and Gammarus crustaceans.

Giles Adams, CRT Volunteer, explained: “When people are out walking by their local rivers they may see riverflies at their mating stage, when they develop wings and rise above the water. But first these fascinating creatures spend a year or two under water in their nymph state, looking a bit like a stick insect. At all stages they are key parts of the ecosystem; food for fish, birds and bats.

“The ARMI scheme asks participants to monitor eight species that are relatively easy for citizen scientists to identify. We wade through shallow water kick sampling, which means we shuffle along kicking the detritus up from the bottom of the river and catch what we’ve disturbed in a net.

“We use a big pippette (like a turkey baster) to put them into a tray with separate compartments (like you’d have your dips and nibbles in at a party), and then count the number of each indicator species.

“The method is standardised, so that the Riverfly Partnership coordinators can compare the results. Anyone can learn to do it, but you need training and proper equipment.

“I enjoy volunteering on Bere Marsh Farm. They have a good bunch of volunteers, and it is satisfying to help out with their conservation work. As a bonus, I can cycle there as I live close by.”

Jenny Ashdown is volunteering on the farm as part of studying towards a level three qualification in Wildlife, Ecology and Conservation at Kingston Maurward College in Dorset. She said: “The riverfly training was fantastic. We were lucky enough to see mayfly hatching and I even had one land on me, which was very exciting.”

If you’d like to get involved in volunteering on Bere Marsh or another CRT farm near you, contact us:


Read more about the Anglers' Riverfly Monitoring Initiative

All images © Nick Dobbs