The health of a river is dependent on many factors, three primary ones being water quality, habitat and flow. Riverfly populations reflect the health of our rivers and still waters. They are sensitive indicators of water quality and commonly referred to as the rivers 'canary'.
The Angler's Monitoring Initiative is a Riverfly Partnership project where trained volunteer groups monitor the water quality of their rivers by recording the abundance of riverfly groups. Should abundances fall below a site specific level the groups alert the relevant statutory body for further investigation. The initiative, launched in 2007, has already led to three successful Environment Agency prosecutions of the companies responsible for the falls in water quality first detected by the volunteer groups.
Reported apparent declines in riverfly numbers are of increasing concern.
Factors that may cause a detrimental impact to riverfly populations, include, amongst others:
Many ponds have been lost in recent years through in-filling, draining or natural succession. Modification of river channels e.g. straightening, causes the loss of critical bank-side and shallow in-stream habitat.
Point source and diffuse pollution
Agricultural run off, high in nutrient levels
Excess nutrients may also lead to large algal growths which smother vegetation and reduce dissolved oxygen levels creating unfavourable conditions for riverflies. The impact of insecticides on aquatic-invertebrates is demonstrated in that a teaspoon full of the pesticide cypermethrin can devastate all life to the volume of water equivalent to an Olympic size swimming pool.
Siltation Soil erosion may lead to unnaturally high levels of silt in watercourses which smother the river bed
Low flows as a result of climatic causes or abstraction. Reduced flow can reduce habitat availability and cause pollutants to become more concentrated.
Climate change & temperature variation
Artificial light may cause disorientation in adult riverflies attracting them away from their natural bankside habitat.