HIGH levels of pollutants have been found in the River Frome, which passes between Frenchay and Downend on its way to Bristol docks, and its tributaries.
Measurements of phosphate and nitrate nutrients were carried out by a team of 193 volunteer ‘citizen scientists’ for the Bristol Avon Rivers Trust as part of its RiverBlitz event.
They took sampling kits and monitored rivers across the Bristol Avon catchment, including the Frome and tributaries the Folly Brook in Emersons Green, the Leap at Leap Valley and Bradley Brook, between Bradley Stoke and Winterbourne in July.
The river conservation charity analysed the 293 samples, and its results show all of those collected in the Downend area showed either high or medium levels of phosphates and nitrates, pollutants which can have harmful effects on wildlife.
BART says the pollutants can enter streams and rivers from a variety of sources, including pesticides and fertilisers washing off fields, waste from livestock, sewage overflows and treated sewage discharges.
BART chief executive Simon Hunter said: “As this presents just a single snapshot of phosphate and nitrate data, it is challenging to single out the cause and source of the particular issue.
“However, what our citizen science data does show is that there is a problem regarding the levels of nutrients entering our watercourse at that given time – in the case of the 2023 Blitz, following a significant rainfall event following a very dry period in summer.
“The causes of high nutrient levels are likely to be as a result of water industry discharges as well as misconceptions from homes and possibly businesses, and impacts from agricultural land-use too.”
Higher levels of nitrates in upstream areas were likely to be linked to farming; phosphate levels – linked to sewage and urban run-off as well as agriculture – were higher downstream.
BART says 89% of sample locations across the region recorded high levels of nutrients, with only one out of 293 showing a low concentration: 83% of samples were high in nitrates and 42% high in phosphates, with levels of both higher than average over previous surveys.
Wessex Water, which is responsible for the region’s waste water, recently featured in a BBC investigation into sewage releases into watercourses during dry weather last year.
A Wessex Water spokesperson said none of the sites were in the Frome Valley.
The spokesperson said: “Phosphates are the main pollutant in the Bristol Avon catchments. Wessex Water has already removed 100 tonnes of phosphate per year from water recycling centres and we’re spending a further £57 million to remove another 70 tonnes by 2025.”
A map showing where samples were taken can be found at bristolavonriverstrust.org/riverblitz.