Latest data on River Test and River Itchen reveals concerning issues

Test and Itchen are no exception to national decline in water quality and flylife

The S&TC Riverfly Census continues to reveal worrying declines in flylife and water quality in rivers across England and Wales, as confirmed by our latest report on the River Test and the River Itchen (the king and queen of our precious chalkstreams).

In our comprehensive Test and Itchen report published today, the results from three years of independent species-level invertebrate data reveal:

  • Significant loss of mayfly species.
  • Low gammarus counts.
  • Worrying impacts from sediment, phosphate and, occasionally, pesticides.

Mayfly and gammarus declines

Comparing historic data with our findings has revealed that both the Test and Itchen have four less mayfly species, on average, than their historical averages. This decline in mayfly species richness, and the worrying low numbers of gammarus, are powerful indicators of an ecosystem in distress.

The flylife in both rivers is far poorer than we would expect for chalkstreams in good condition  - let alone these SSSI (Sites of special scientific Interest) and SAC (Special Area of Conservation) rivers.

Mayfly species have declined from an average of 12 to 8 (33.3%) on the Itchen and 11 to 7 (36.36%) on the Test, over the period from the late 1970s/early 1980s to today.

The current levels are also well below local targets of 10 mayfly species - targets agreed with the Environment Agency for what would be expected in a healthy river.

Gammarus, a key staple of the aquatic food chain, is also well below our 500-target level at most sites (historically, gammarus counts went into the thousands).

Excess sediment and phosphorus

Our report reveals the extent that chemical, phosphorus and sediment pollution are impacting the invertebrate community in both the Test & Itchen.

It is clear that a reduction of sediment and phosphate inputs (from point and diffuse sources, including septic tanks, agriculture, sewage treatment works, industry, etc) are essential to conserve these rivers.

Importance of the S&TC Riverfly Census

Lauren Mattingley, S&TC’s Science Officer, explains why data like this is so important:

“We frequently hear stories and concerns about missing flylife and lack of fish compared to the 'good old days', but anecdotal evidence has little weight in environmental decision making.

The Riverfly Census was launched as a ‘myth-busting’ tool to collect much needed high-resolution, scientifically robust data about the real state of water quality in our rivers.

Switching from opinion to fact-based evidence gives us real power to drive national and local improvements to our waterways.

“The Test & Itchen report is a fantastic example of why we need to break away from data ‘silos’.

The Riverfly Census data tells a story on its own, but when linked up with additional local invertebrate and phosphorus monitoring data, we can really start to grasp the pressures on these rivers.

The environment is complex, and stressors rarely work in isolation, so why would we conduct monitoring this way?”

Turning science into action

The Census is no mere academic exercise. We are using this powerful data to inform and build effective strategies which improve wild fish habitat:

  • We are acting on the Census results to improve water quality in these rivers, working with stakeholders in the area.
  • We are tackling known sources of pollution; such as the Bakkavor salad washing plant on the Itchen headwaters, and intensive watercress farming on both the Test and the Itchen.
  • Our findings on the Itchen impelled us to challenge the EA under the Environmental Damage Regulations. We are awaiting the EA’s response.
  • To share the Riverfly Census results from the Test and Itchen and drive further improvements to these rivers, we will be holding a workshop on 12th February 2019. A key aim of the workshop will be to highlight knowledge gaps and develop next steps with a range of stakeholders, regulators and scientists. Please contact Lauren (lauren@salmon-trout.org) if you or your organisation would like to book a place at the workshop.