Warm temperatures raise algal bloom risk in rivers and coastline

As temperatures start to climb, the Environment Agency is warning beachgoers and river users that sightings of algal blooms are also on the rise across Northamptonshire. 

Hot and sunny weather typically triggers algal blooms and as these decay, they are often mistaken for pollution. As the mass of algae breaks down it can reduce dissolved oxygen levels in our waters leading to fish becoming distressed and, in some cases, dying. 

Ben Thornely, Environment Agency Manager for Lincolnshire and Northamptonshire said: “Every year when temperatures rise, we receive many reports of suspected sewage pollution, at coastal waters in particular, that are in fact the breakdown of algal blooms.

“In freshwaters, particularly lakes, blue green algae (cyanobacteria) especially thrive in warm conditions and has the potential to be harmful by forming blooms and scums which can be highly toxic to humans, fish and animals.

“It is easy to mistake algae for sewage, particularly as both have an unpleasant smell, but foam on the water’s surface or on the beach is more likely to be the result of an algal bloom breaking down.”

Blooms can discolour the water, varying between blue-green, green or greenish brown, and should be avoided as they can be toxic and can lead to a variety of symptoms including vomiting and diarrhoea. For dogs and livestock, ingestion of scums can be fatal, so pet owners and farmers need to keep animals away from and out of the water.

Here are a few tips to help tell the difference between algal blooms and pollution:

• Algal blooms generally occur between April and August.

• Long lines of algal foam can often be seen off headlands lying parallel to the coast.

• In rough conditions thick mats of foam may be created on the shoreline by wave action.

• Stormwater overflows tend to cause a grey discolouration of the water and often have an origin such as a pipe or outfall, where the discolouration is strongest.

• Sewage discharges can contain fats and oils causing waves to flatten around it and sometimes attract seabird flocks.

If members of the public are concerned, they can report any algal blooms (or pollution) to the Environment Agency’s 24 hour freephone incident hotline on 0800807060. Once an algal bloom is confirmed by the Environment Agency, that information is sent to the landowners and other statutory bodies so that any necessary action can be taken.

Further guidance and advice has also been published on the Gov.uk website: https://environmentagency.blog.gov.uk/2022/06/22/telling-the-difference-between-an-algal-bloom-and-sewage/.

On the Environment Agency’s YouTube channel, there is also a video explainer on spotting, reporting and staying safe around algal blooms here: https://www.youtube.com/watch?v=dB1OjKWVB-o