What exactly are invertebrates?
Invertebrates are simply animals without a backbone. In a chalk stream, they include an extraordinary variety of small creatures that live amongst the gravel, aquatic plants and river margins.
Look closely and you might find mayfly nymphs, stonefly nymphs, caddisfly larvae, freshwater shrimp, water beetles, snails, worms and midge larvae. Some are tiny and easily overlooked, while others are surprisingly distinctive.
These creatures are an essential part of the chalk-stream ecosystem. They provide food for fish, birds and other wildlife, and their presence and abundance can tell us a great deal about the conditions in the river.
Different species also have very different tolerances to environmental change. Some are particularly sensitive to pollution, sediment, low flows and changes in water quality, while others are much more tolerant.
That makes the invertebrate community a kind of living indicator of river health.
And in the smaller headwaters and Winterbourne streams, the lucky monitor may encounter some of our rarer chalk-stream specialists – species whose presence is a reminder of just how unusual and internationally important these habitats are.
So, what is a kick sample?
A standard Riverfly survey involves placing a fine-meshed net on the riverbed and disturbing the gravel, vegetation and sediment immediately upstream. The current carries the small creatures living in the river into the net.
The process samples the different habitats within the reach – perhaps clean gravel, aquatic vegetation and the margins – before the contents of the net are examined in a tray.
Among the leaves and gravel will be the tiny animals that spend much of their lives hidden beneath the surface.
Riverfly and SmartRivers
There are several approaches to invertebrate monitoring.
Riverfly Monitoring Initiative (RMI) provides a relatively simple way for trained volunteers to monitor sites regularly. Eight key invertebrate groups are counted, creating a score that can be compared with an established trigger level. A significant change can provide an early warning that something may have happened in the river.
SmartRivers takes the process further. Samples are normally collected in spring and autumn and analysed in much greater detail, with invertebrates identified to species level wherever possible. The resulting data can help identify potential pressures associated with sediment, nutrients, chemicals, flow and organic pollution.
In simple terms, Riverfly can help tell us “has something changed?”, while SmartRivers can provide much more detailed evidence to help investigate “what might be causing the change?”
Every sample tells part of the story
Before sampling begins, volunteers will often photograph and record the condition of the river – its width and depth, flow, aquatic vegetation, gravel and fine sediment, bankside cover and other features.
And no two samples will ever be exactly the same.
One year a reach may be dominated by aquatic vegetation; another may have exposed gravel and accumulated fine sediment. Flow conditions, water levels and habitat can all change.
That is why repeated monitoring is so valuable.
A single sample provides a snapshot. Samples taken from the same location over months and years begin to create a much more powerful picture of how the river is changing.
The biological information can then be considered alongside water temperature, flow, chemistry, rainfall, land use and other observations to help identify potential impacts – whether from a localised point source or pressures operating across the wider catchment.
Who is doing this work?
WildFish — SmartRivers
WildFish – SmartRivers runs the national SmartRivers programme, with spring and autumn invertebrate sampling and species-level analysis. Its open-access national database brings together data from rivers across the UK, creating an increasingly valuable resource for understanding changes in river biodiversity and potential pressures.
Test & Itchen Association
The Piscatorial Society
Upper Itchen Restoration CIC
Other groups involved in monitoring include:
Wessex Rivers Trust has also undertaken detailed Catchment Invertebrate Fingerprinting work on the Test, Itchen, Meon and Hampshire Avon.
And these are just some of the organisations involved. There are many smaller river groups, angling clubs and community organisations carrying out their own monitoring across Hampshire and the wider UK.
Together, these volunteers are creating something much bigger than a collection of individual samples. They are building a long-term biological record of our chalk rivers – one that can help us understand change, identify potential pressures and provide evidence for action.
A huge thank you
At The Chalk River Project, we want to say a very big thank you to everyone who gets into the river, often in less-than-ideal conditions, to collect this information.
Every sample adds another piece to the jigsaw.
Every photograph records a moment in the life of the river.
And every year of monitoring makes the next year’s results more meaningful.
Three minutes in a river may seem insignificant. But multiplied across hundreds of sites and repeated year after year, those three minutes become a very powerful source of evidence.
So, the next time you see someone standing in a chalk stream, vigorously kicking the riverbed into a net, don’t assume they’re simply looking for bugs.