The UK may be underestimating how poor the water quality is in its streams and rivers, according to scientists from Lancaster University.
The ten-year project studied the composition of diatoms,which are single-celled algae used as indicators of the level of nutrients in the water.
Diatoms are particularly good at revealing levels of phosphorus, which often comes from fertilisers used in agriculture and from wastewater, may cause harm to wildlife in rivers and the oceans.
Typically, environmental regulators monitor diatom communities twice a year, in spring and in autumn. But the new study, published in Scientific Reports, shows that the diatom community varies throughout the year and suggests that stream pollution can be particularly bad in winter.
Dr Maria Snell, a former researcher at the Lancaster Environment Centre and lead author of the paper, took monthly measurements in three tributaries of the River Eden in Cumbria over seven years.
This work showed a regular, seasonal variation in the makeup of the diatom communities, with these communities indicating significantly more phosphorus in the streams during winter.
Professor Phil Barker, co-author of the paper and director of the Lancaster Environment Centre, added: Water quality policies have tended to ignore the crucial winter season and yet we expect UK winters to get wetter in the future.
‘We must work closely with farmers to help reduce pollutant movement from land to water during this critical season, and with governments to ensure climate change is better captured by future legislation.
The study was part of theRiver Eden Demonstration Test Catchment(DTC) project, funded by Defra and led by Lancaster University.
Last week, research by Bangor University and Friends of the Earth found microplastic pollution has been found in some of Britains most iconic and remote rivers and lakes.
The study looked at ten sites, including lakes in the Lake District, waterways in the Loch Lomond and Trossachs National Park, a wetland and Welsh reservoir, and found microplastics in every one.
Researchers used a fluorescence lighting system and were able to identify and count microplastic pollutants per litre of water, such as plastic fragments, fibres and film.
The waterways surveyed (including pieces of plastic per litre of water) were: