River Avon: Riverfly Census Results

River Avon Riverfly Census

The results are in from our ground-breaking Riverfly Census campaign for the River Avon. View the results below and read more about what we found, why it is important, and what we are doing next!

What is the River Avon Riverfly Census campaign about?

Our campaign is to reverse the decline in water quality in the Avon. Water quality (or the lack of it) determines the ability of a river to support life.

Our Riverfly Census along the River Avon has revealed significantly less water insects than should be present, trending downwards by up to 50% since 2015, due mainly to excessive phosphorus and sediment in the water.

How does this campaign affect salmon and trout?

Water insects are an accurate measure of water health, and in the River Avon (designated a Special Area of Conservation) they are under significant pressure from phosphorus, sediment pollution and pesticides. We know this from our independent professional surveying - our 3 year-long Riverfly Census - which is unique to S&TC and highly rigorous across the UK.

Specifically, our research has unearthed a surprising decline in Blue Winged Olive flies, a crucial part of the river food web and a staple in any chalk stream. Loss of such an important species definitely indicates a cry for help in the Avon, and directly impacts the health and abundance of salmon and trout. Other stats show distributing downward trends:

  • Over 60% of sites showed worrying chemical footprints in Autumn 2017
  • Over 50% decrease in numbers of different mayflies at Stratford Bridge since 2015
  • Over 52% decreases in the amount of all species at Ham Hatches since 2017

We have summarised these findings into a simple one-page fact sheet, perfect for sharing. Please view this here.

Alternately, we welcome you to view and share the full report and data sheet.

Phosphorus and sediment do occur naturally in rivers in small amounts, but in excessive quantities are lethal to water insects. They promote algal growth, which chokes the river of life and negatively impacts egg development of invertebrates through suffocation. We believe these stressors are responsible for the shortage in these essential insects. The EA have similarly demonstrated that there is too much phosphorus in the river from their own monitoring.

Excessive quantities of phosphorus and sediment can be caused by many things, including fertilisers, septic tanks, road run-off, loose soil from farming practices, dust, dirt, and sewage. Indeed, the Amesbury and Ratfyn Sewage Treatment Works have had an increasing upward trend of phosphorus in their final effluent (2012-2017 data), which we suspect is a large contributory factor.

Overall, the River Avon ranked No.1 in terms of health and vitality in our 2015 Riverfly Census; now in 2018 it has significantly declined and taken a turn for the worst. At some sights, mayfly species had declined almost 40% since 2015, and Stratford Bridge declined by over 50% in 2017 compared to 2015 & 2016.


View the fact sheet, report and data here:

What is our plan to tackle these issues?

At S&TC, our entire model is fact based campaigning. As such, our full technical report from the Avon has been taken to the Environment Agency (the regulator) and other river stakeholders (such as Wessex Water). We are seeking to influence change by finding more conservation friendly ways forward.

Together with SADAC, we have formally registered our concern with the EA that there is too much phosphorus in the river. We are due to meet with them imminently to discuss their response to our request for action.

A nutrient management plan has been developed by the EA and Natural England to address poor water quality caused by phosphorus contributions from the upper catchment, but we are not yet seeing significant results.

We have therefore met with Wessex Water to present our data and concerns regarding the Amesbury and Ratfyn Sewage Treatment Works, and we continue to pressure them to improve discharge.

The next step is further research, to strengthen our case and force the EA to listen. 

How can you help?

The invertebrate data has indicated that the main problem is phosphorus, so we now need further, more specific, independent data to move forward with the EA and produce real change.

We need to raise money to carry out high-resolution phosphorous monitoring on the River Avon, which involves placing chemical monitoring units at specific sites. We already own these units, but sampling costs at each site are upwards of £3,000 a year, and we need to run at least 4 sites (including monitors above and below the sewage treatment works).

We are looking to individuals, businesses and organisations local to the Avon, or passionate about maintaining this iconic stretch of river, to help us meet this goal. Please support us in protecting one of Britain’s finest and most vulnerable chalk streams. Your funds help us in the following way:

  • £14 runs a sampler at one site for one day
  • £50 analyses one sample from one site
  • £100 runs a sampler at one site for a week
  • £3,000 runs a sampling site for an entire year

Additionally, it is important to note that we are taking a much wider view of the issues on the Avon, beyond just sewage. A wider problem, in our view, is bad agricultural practices; which we continue to research into - both the problems and potential solutions - and work with the EA to influence change. This is where longer-term support of our work is vital; and we gratefully thank our members for their ongoing help.

How else can you support us?

In many places the river still looks beautiful, but of course you can’t really see phosphorus. So alongside funding our research, we also need to educate people on ‘invisible threats’ and what is happening beneath the surface. The sharing of this research is the first step in highlighting, and educating on, these unseen issues in the Avon.

Action is required NOW. Over the next 3 to 5 years the pressure on the river will only increase as we expand as a population (for example, there is extensive building in the Avon Valley, and the army is soon re-basing at Salisbury). This means increased pressure on sewage works and increased run-off into the river, so the EA urgently need to establish control.

Please assist us in spreading the word about the opportunities to improve the River Avon by sharing this content with locals, anglers, nature and water enthusiasts, wildlife lovers, relevant NGO’s and charities, and anyone else who may be interested or able to assist us. Download everything you need below:

We rely on your support to protect wild fish and the places they live.

By donating or joining as a member you will be making a huge contribution to the fight to protect the UK's waters and ensure a sustainable future for wild fish.