Blue Green Algae
Blue Green Algae: What you need to know
Blue Green algae, or cyanobacteria, are naturally occurring organisms found in many lakes, including Windermere.
While they play an essential role in freshwater ecosystems, under certain conditions, they can form dense blooms which may pose a risk to people and animals. This page explains what they are, what to do if you suspect them and how to stay safe while enjoying Windermere.
Blue-green algae are microscopic organisms found naturally in lakes, rivers, and ponds. Despite the name, they’re technically bacteria, specifically cyanobacteria, which behave like plants by using sunlight to grow.
Most of the time, they’re present in low numbers and go unnoticed. But when conditions are right – especially in summer, they can multiply rapidly into “blooms” and turn the water green, blue or brown. You might see cyanobacteria as:
- Wisps or foam
- Paint-like streaks on the water’s surface
- Cloudy green ‘pea soup’ like appearance
- Lumpy or oily-looking clumps near the shore
Not all algae are harmful, and blue-green algae can often be mistaken for Duckweed or filamentous algae, but it’s best to assume a bloom could be dangerous and take precautions.
Why Does it Happen?
Blue-green algae (cyanobacteria) are a natural part of freshwater ecosystems, but under the right conditions, they can grow rapidly into harmful blooms. Three key factors influence when and where blooms appear:
Nutrient levels
Excess nutrients like phosphorus and nitrogen feed algae. These nutrients enter the lake from a range of sources, including treated and untreated wastewater, septic tanks, surface runoff, and fertilisers. Reducing nutrient inputs is one of the most effective ways to reduce the frequency and intensity of blooms.
Weather conditions
Prolonged warm, calm and sunny weather provides ideal conditions for algae to thrive. Long daylight hours, stable water temperatures and still conditions allow algae to remain in the sunlit surface layer of the lake, increasing their rate of growth.
Water movement
In lakes like Windermere, periods of still water mean algae are less likely to be dispersed by wind or currents. Instead, they can gather and float to the surface, often accumulating in sheltered bays or near the shoreline. These visible concentrations are what we refer to as “blooms” found in open waters or surface scum typically accumulated inshore.
These conditions are more common in summer and autumn, especially during dry, calm spells.
Is it Harmful?
Certain types of blue-green algae produce toxins that pose significant risks to humans and animals, particularly if ingested or if they come into contact with open wounds. Exposure to these harmful blooms can lead to skin rashes, eye irritation, and stomach upset. Ingesting large quantities can result in even more serious health issues for both people and animals. It’s essential to be aware of these dangers to protect yourself and your pets. If you spot a possible bloom:
- Avoid contact with the water
- Keep pets out of the lake
- Don’t let dogs drink the water
- Wash hands after being near the shore
- Report it so others can stay safe too
Blooms can occur unexpectedly and may drift with the movement of wind and water currents. It is important to note that just because one section of the lake appears to have a bloom, this does not imply that the entire lake does.
How to Report a Bloom
You can help protect others and the environment by reporting sightings:
Call
The Environment Agency operates a free 24-hour incident hotline. If you spot a possible blue-green algal bloom, please record the time, date, and location, and, if possible, take a photo.
Bloomin’ Algae
Download and use the free Bloomin’ Algae App from the UK Centre for Ecology & Hydrology. You can download the app directly from Google Play or the App Store.
Spot. Snap. Report
The Environment Agency is developing an online reporting tool allowing users to submit and track environmental concerns easily. This platform aims to enhance transparency and improve the efficiency of reporting processes. Please check back soon for more details.
All reports are sent to the local Environment Agency team for investigation and confirmation. If blue-green algae are found, landowners and stakeholders are notified, and it is recommended that signage be put in place.
Useful Resources
- Government Guidance on Blue-Green Algae
- Spot, snap, and report blue-green algae | Engage Environment Agency
- EA Blue-green algae leaflet
- Bloomin’ Algae | UK Centre for Ecology & Hydrology
- Storm overflow map | United Utilities – Better Rivers – Disclaimer: overflows don’t always result in BGA blooms, but they may contribute.
- Bathing water quality – Bathing water quality assessments in England focus on Escherichia coli (EC) and Intestinal Enterococci (IE). These bacteria are used to determine the presence of faecal matter, whether from human or animal sources, in the water. Blue-green algae checks are not included unless deemed necessary by assessors.
- Understanding Blue Green Algae – blog
- A Changing Windermere – Summary Report
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