A “putrid” layer of bright yellow algae on the surface of the water at a protected nature reserve had raised fears of pollutants at the site.

But authorities have reassured Canterbury residents that the striking display at Stodmarsh National Nature Reserve near Hersden is nothing to worry about.

Canterbury river warden Sian Pettman, was shocked to see the viscus coating of algae on the lake when she visited the site last week.

“The word to describe it is putrid,” said Mrs Pettman.

“It looks extremely unhealthy and it makes me very concerned about what is in the water, what is causing it and what effect it is having on the wildlife.

“To be honest is looks like vomit.”

There were fears that the algae, which covered a large portion of the lake, might be evidence of eutrophication – a process by which the presence of high concentrations of nitrogen and phosphorus leads to excessive growth of algae in a body of water.

This algae then blocks the sunlight from reaching plant life below the water’s surface, preventing them from photosynthesising and in turn depriving other wildlife in the water that relies on the plants to survive by decreasing the concentration of oxygen in the water.

Eutrophication can occur naturally but it can also be caused by pollution when sewage or fertilisers contaminate fresh, salt, or brackish water.

Guidance from the Environment Agency (EA) explains that in freshwaters, blue-green algae (cyanobacteria) sometimes form blooms and scums which can be highly toxic to humans and, for animals even fatal.

But a spokesperson for Natural England – the non-departmental public body that owns the Stodmarsh Nature Reserve – said the algae at this site is not dangerous.

“The naturally occurring blanket weed (filamentous algae) on the main lake at Stodmarsh National Nature Reserve is not considered to pose any adverse health risks to people or wildlife.

“The growth of the non-toxic weed has increased due to the recent warm temperatures and we continue to closely monitor the situation for any impacts on the water environment at the reserve."

A representative from the EA added that the unusual yellow colour of the algae is due to the recent hot and sunny weather – the ordinarily green algae has been bleached yellow.