Wye Algae PhD Study

Monday 17th July 2023





There has never been such a comprehensive study into the cause of algal bloom before. The project has made good progress in determining the diversity of the Wye’s algal and bacterial communities and the combination of nutrients that are required to fuel algal blooms. It found that in 2022 several parts of the catchment had all the conditions required by harmful cyanobacteria species.

There are two main causes of these nutrients flowing into the river: diffuse – via stock access, soil loss, overland flow and drainage systems and point source – where the pollution comes from a single source like a sewage plant outflow. The way the concentration levels of the nutrient changes over time and river flow indicates how they are likely to have entered the river. The data suggests that high nitrate inputs from the Lugg into the Wye is coming from diffuse pollution. But until we collect more data we are not yet able to say if the high total phosphorus and soluble reactive phosphorus inputs from the Lugg are likely to be from point source pollution.


The research also shows how the algae responds to changes in nutrients. They found a high diversity of algae and bacteria in 2022 with no dominant species. Green algae and diatoms were the most abundant groups of algae. However, interestingly, across all sites a succession in cyanobacteria species was evident throughout the sampling period. Notably, the relative abundance of cyanobacteria commonly associated with harmful algae blooms, was highest on the River Ithon, followed by the River Lugg.

Cardiff University have also been analysing types of animal faecal bacteria (coliforms) found in the river. Initially, at a broader (genus) level, they will be able to tell if they are from humans, livestock, or poultry, but further work at a more detailed (species) level will allow firm conclusions to be made on the source of each of these coliforms entering the river.

This research should ultimately benefit the Wye and Usk. As the study progresses WUF are looking to develop a model which will both act as an early warning system for bloom events and allow us to work with others to deliver the changes required to reduce the risk of harmful algae blooms occurring.

We cannot thank enough those who have so generously supported this ground-breaking work so far. We have 2 years funding in place and are seeking the funding for the final year.

Wednesday 14th December, 2022 

The algal blooms in the River Wye have made the headlines and exposed the threat they are to our rivers. Since then, we have partnered with Cardiff University to conduct the Wye Algae PhD, a project to which so many of you kindly donated and helped fund.

With the first year of the project complete, Cardiff University is now analysing the first set of data taken from 14 sites along the Wye. Although the results are not yet conclusive, here’s what we do know so far:

The extremely dry spring and summer of 2022 resulted in low flows, however, no suspended algal bloom occurred despite the survey detecting high nutrient concentrations. Two areas maintained high levels of phosphate throughout the sampling season; one being at the bottom of the River Ithon and the other at the bottom of the River Lugg. Also, there was a high bacterial diversity which helps prevent one species from out-competing another. This suggests that the conditions may not have been quite right for just one species to become dominant to form algal blooms.

Could this summer’s low water levels be what prevented the formation of an algae bloom? Did the extensive algal growth on the bed use up the nutrients? Or could there be another factor which limited the ability of suspended algae to thrive in our river system in the summer of 2022?

Why are algal blooms a threat?

Severe algal blooms turn the water into a pea-green or brown blanket, reducing the access of light to the rivers’ plants such as Ranunculus, otherwise known as water crowfoot. It is a highly protected and keystone plant species that can help raise water levels in the summer, provides shelter for fish and invertebrates and ‘filters’ the water passing through it. Ranunculus is a key habitat in our river systems and is integral to maintaining healthy fish stocks. Also, when algal blooms die or respire overnight, they cause oxygen levels in the river to fall, which can lead to stress and mortality of fish.

There is still much to learn, but with the continuation of this study funded by our generous donors, we aim to unveil the triggers of algal blooms in the River Wye and River Ithon systems. Please consider donating to our Wye Algae PhD project which will fund the third and final year. Until then, stay tuned for more information about this year’s results.

Thursday 18th August, 2022

The Wye Algae PhD is now officially underway!

With the first samples taken in June, this three-year project hopes to unveil the triggers of algal blooms in the river Wye and river Ithon system.

Water samples are taken every two weeks to determine which nutrients and other environmental variables trigger algal blooms. These samples and their results will act as a useful tool for finding intervention solutions for improving the water quality of the river Wye.

The type of nutrients determined will include total phosphorus, soluble reactive phosphorus, nitrate, ammonium, and silicate. Organic phosphorus and nitrogen fractions will also be determined, as well as range of other environmental variables such as temperature.

We would like to thank all of those who kindly donated towards the first and second year of the Wye Algae PhD project. The first set of results are currently being analysed, so please stay tuned!

Thursday 7th April, 2022

Great news, we have the funds for the study, which will now start in June 2022.

Our thanks to everyone who has supported this initiative. We look forward to seeing the results as soon as they start coming in.

Thursday 27th January, 2022

In partnership with Cardiff University, the Wye & Usk Foundation is setting up a PhD study to establish the causes of the Wye’s severe algal blooms.

The study is due to start in March and run for three years. It will provide the quantity and quality of data needed to show causation with certainty.

More information on the Wye Algae PhD 

Donate to the Wye Algae PhD appeal

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