Riverfly Census reveals pollution concerns for River Wensum, says Salmon and Trout Conservation UK

PUBLISHED: 13:39 17 August 2017 | UPDATED: 13:39 17 August 2017

The River Wensum. Picture: Matthew Usher.

The River Wensum. Picture: Matthew Usher.


Conservation efforts have so far failed to improve pollution levels on the River Wensum, according to an updated survey of riverflies – regarded as a key indicator of river health.

The Salmon & Trout Conservation�s Riverfly Census says loss of flylife such as blue-winged olive (Serratella ignita) is a clear indication that pollution is affecting the health of a river. Picture: Stuart CroftsThe Salmon & Trout Conservation�s Riverfly Census says loss of flylife such as blue-winged olive (Serratella ignita) is a clear indication that pollution is affecting the health of a river. Picture: Stuart Crofts

Fisheries charity Salmon and Trout Conservation UK (S&TC) has completed the second year of its three-year Riverfly Census, which aims to assess the health of 12 protected rivers by measuring invertebrates which are a vital part of the aquatic food chain.

Last year, despite its designation as a Special Area of Conservation (SAC), the Wensum was ranked bottom of this national survey.

This year’s report found the richness of mayfly species is still “below the level that would be expected for the middle reaches of a healthy chalk stream” at all five survey sites: Doughton Bridge, Fakenham Common, Pensthorpe Park, Sennowe Bridge and Bintree Mill.

In spring and autumn, sediment was also “at or above the level considered to have a detrimental impact on the invertebrate community” for all five sites, while phosphorus levels were at or above the level of concern at four sites in spring, and two in autumn.

Wensum Valley farmers visited Pensthorpe Nature Reserve to discuss the effect of agriculture on the fish life in the River Wensum. Picture: Ian BurtWensum Valley farmers visited Pensthorpe Nature Reserve to discuss the effect of agriculture on the fish life in the River Wensum. Picture: Ian Burt

The report says the results show the Wensum’s water quality is under “severe pressure from sedimentation and phosphate”, which could be attributed to a range of sources such as agricultural and roads run-off, poorly treated sewage, septic tanks, and new developments.

Last year, the Upper Wensum Cluster Farm Group was formed in a bid to reduce the impact of agriculture on river habitats and wildlife, bringing together 17 farmers and landowners to co-ordinate conservation efforts across 6,000 hectares of land.

Dr Janina Gray, head of science with S&TC, said it would take time for their efforts to be reflected in a resurgence of riverfly activity.

“The results from the 2016 spring and autumn counts are concerning and reflect an increasing level of pollution entering this important chalk stream,” she said.

“Although the Wensum story is mostly negative, we were very encouraged by the passion of the farmers to help restore the river when we met last year. “It will take time to get the river back to a healthy condition, but I am sure the dedication of the farmers working on their stretches of the Wensum will help to ensure ecological improvement occurs over the next few years.”


Heidi Smith is business manager for Norfolk FWAG, the county’s farming and wildlife advisory group, which co-ordinates the Wensum cluster.

“It’s obviously very disappointing that the results have not changed despite the continued efforts of farmers in the area working within the Broadland Catchment Partnership and cluster farm group,” she said.

“Farmers are very aware of the need to prevent run-off of water from agricultural land into the Wensum. This water transports silt, nutrients and pesticides with it which are thought to be partly what is causing the low riverfly counts.

“When heavy rainfall washes nutrients, pesticides and soil off a farmers field, this is effectively carrying away money. No farmer wants to see that so they have every incentive to take measures to stop this happening. The Upper Wensum Cluster Farm Group has met several times since the last riverfly census, to discuss measures to prevent run-off and share best practice. This is an issue that is taken very seriously within the farming community.”


Conservation advisers at Norfolk FWAG said Wensum valley farmers can implement measures to reduce run-off and pollution, including:

• Ensuring crops which disturb the soil such as maize and potatoes are not grown on land which slopes down to the Wensum.

• Planting catch and cover crops on land which would otherwise be left bare, to soak up nutrients and bind the soil together.

• Disrupting vehicle tramlines in fields, so they cannot act as pathways which deliver water and run-off quickly to the river.

• Leaving generous buffer strips alongside watercourses to slow down and absorb run-off.

• Moving filed entrances to drier locations to prevent the land becoming churned up.

• Installing silt traps and drain diversions – these measures are known as rural SuDS (Sustainable Drainage Systems). Norfolk FWAG currently has money available from the Environment Agency to invest in rural SuDS in the southern Broads and Brecks catchments.


Nick Measham, campaign manager at S&TC, said understanding why riverfly numbers, such as blue-winged olives, are declining is the first step in the process of safeguarding the aquatic environment.

“The evidence from our census is irrefutable,” he said. “Increased phosphates and fine sediments are having a disastrous impact on invertebrate communities in our rivers.

“We would like local people to help change the way our rivers are managed by demanding better protection and monitoring. We would urge them to get in touch with us so that we can take forward issues with local MPs or the Environment Agency.

“This is a call to arms to everyone to help save our rivers and the important aquatic wildlife that clean water supports.”

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