Blue Green Algae and Swimming: Summer has arrived in the Lake District and locals and visiting swimmers alike are enjoying exceptional swimming conditions in one of the most diverse wild swimming destinations in the world. In our local, lake Windermere alone we enjoy 3 Environment Agency Designated Bathing Areas with exceptional water quality. However, while we open water swimmers love the calm and sunny weather, conditions are also perfect for the growth of blue-green algae (Cyanobacteria), some forms of which can be harmful to both people and animals.

Why is blue green algae present?

In the Lake District the presence of high concentrations of algae is a natural annual event especially in the larger lakes. These tend to be richer in nutrients which, when coupled with warm and calm weather, provide the ideal conditions for increased algal growth which often leads to the formation of algal blooms (visible as clumps and scum on the water surface). It is important to realise that the presence of blue-green algae is not a bad thing in itself. Together with other algal groups they are important contributors to the aquatic biology of fresh and marine waters. They are primary producers that:

• convert sunlight to energy by photosynthesis • release oxygen and carbon dioxide into water • take up minerals • produce food chain supporting substances

Not all blue-green algae are toxic (toxic forms are in the minority), and blue green algae and swimming can co-exist, but there is no way to tell whether a bloom is toxic by looking at it (this requires laboratory testing). As swimmers, we must err on the side of caution and avoid areas of excessive algal blooming.

The Environment Agency is working with local businesses to reduce the levels of excessive nutrients entering the catchment area of our big Cumbria Lakes. In the long term should help to reduce the incidence of algal bloom formation.

What do blue-green algal blooms look like?

Blooms and scum can have the appearance of paint, jelly or small clumps and tend to rise to the surface during calm weather conditions. Scum colour varies because algal pigments differ between species, depending on the nutrient supply, light intensity and age of the bloom. Scums may be blue-green, grey-green, greenish-brown or occasionally reddish-brown. The persistence of scums also depends on which species are present. Some form quickly on calm days, but are rapidly dispersed if wind and wave action increases.

Some blue-green algae are also sensitive to water temperature and can sink to the bottom of a lake in warm weather (apparently disappearing) and resurface during colder conditions. Because there are so many factors affecting its distribution and movement, its presence is very hard to predict.

Microscopic Blue Green Algae and Swimming

Blue green algae and swimming, who is at risk?

Any person or animal coming into contact with algal scum is at risk from the potentially harmful effects of toxic blue green algae if it is present in the scum. This includes boaters, bathers, paddlers, dogs and of course, we swimmers. Green, scummy and smelly water is usually enough to put anyone off swimming but those who do, either by design or by accident can suffer from a wide range of illnesses. Dogs and very young children are particularly at risk, due to their relatively small size and their enthusiasm for messing about in the water.

In extreme cases dogs can die from exposure to toxic algal blooms as they tend to ingest relatively large volumes of algae when retrieving balls and toys from the water as well as when licking themselves clean afterwards. If you dog experiences vomiting and diarrhoea or breathing difficulties after being near water, call your nearest vet immediately.

Although most cases are very mild, illnesses experienced by people who have swam through or swallowed algal scum include skin rashes, eye irritation, vomiting, diarrhoea, fever or cold like symptoms and muscle and joint pain. These conditions have not led to long-term effects or death but in some cases, the illnesses were severe. Although algal scum isn’t always harmful, avoid contact with it and the water close to it.

blue green algae and swimming dogs

Blue green algae and swimming, protecting yourself

Common sense and avoidance are the best ways to protect you and your family (including your pets) from the potentially harmful effects of toxic blue-green algae. If it looks and smells bad, stay out. In the Lake District we have hundreds of excellent swimming locations that remain free of algal blooming, take a look at this article for some alternative swimming ideas: Where to swim in the Lake District

Bear in mind that harmful blooms aren’t always large and dense and can sometimes cover small areas of a lake with little visible algae present. Before entering the water, take a good look at the lake and check for algae in the water column or on the shore-line to help determine if a bloom is or has been present. Algal blooms and scum are often concentrated by the action of the wind, so be more vigilant during on-shore, windy conditions.

If you or your pets do come into contact with blue-green algae, wash it off with fresh water and soap as soon as you can.

The Environment Agency are very good at keeping user groups (such as ourselves at Swim the Lakes) informed so that we can spread the word of any threat to outdoor swimmers. Lake owners are responsible for warning users and erecting signs and restricting access if necessary. Due to the unpredictable nature or algal blooms, this can sometimes take the form of a blanket warning.

Blue Green Algae and Swimming in tarns

Toxic Blue Green Algae and Swimming: Key points

1. You can’t tell if it’s toxic, but if it looks and smells nasty, go and swim somewhere else and report it to the Environment agency on their 24 hour hotline: 0800 80 70 60. If in doubt, stay out.

2. Keep babies, toddlers and family pets out of the water if it looks even vaguely suspect.

3. Blanket warnings may be issued for an entire lake, even though only a small area of that lake may be affected. Use your common sense and seek out clear areas for swimming, or choose another lake… we have lots of lakes, rivers and tarns that are not affected.

4. During windy weather upwind shorelines are often free of blooms, whereas downwind shores can suffer from concentrated algal blooms due to the action of the wind blowing the blooms downwind. Avoid these areas when warnings are in place.

5. If you think you may have swam through a toxic algal bloom, wash yourself off in fresh water as soon as you can and see your doctor immediately if you show any of the more serious symptoms mentioned above.

In our experience the worst symptoms experienced after having swum in algal blooms, is some minor skin irritation and itchy eyes post-swim, not unlike hay fever symptoms. I hope that this article will allow you to make sensible decisions about where to swim when algal blooms are present, and to help to spread the word about suspect areas of water effectively. The information in this article has been sourced from personal conversations with members of the Freshwater Biological Association (based here on the shores of Windermere) as well as with local Environment Agency officers .

Enjoy your swimming, but swim safely.

Pete Kelly
Swim the Lakes

Related Links:

Where to swim in the Lake District

Guided Swimming in the Lake District

Introduction to Open Water Swimming Courses