Blue Green Algae

Information about blue green algae.

What is blue-green algae?

Blue-green algae are tiny organisms which occur naturally in lochs, ponds, reservoirs, and rivers. They commonly occur during periods of prolonged hot weather but sometimes occur at other times of the year. Waters, which have been affected by agricultural, domestic or industrial discharges, can be prone to developing blue-green algae, but they can also occur naturally.

In still waters the algae can multiply to such an extent that they discolour the water which then appears green, blue-green, greenish brown or dark brown. Sometimes a scum may form on the surface. This scum can appear in different places at different times, but is most commonly found at the water's edge or shore line.

How do blue-green algae affect humans and animals?

Some, but not all the blue-green algae produce toxins or release these into the water. It is not possible to tell which algae do or do not produce toxins simply by their appearance. Laboratory analysis is needed for this. Therefore, it is advisable to regard all algal scums as potentially toxic.

The toxins of blue-green algae can cause deaths of animals that come into contact with algae, either through drinking contaminated water, swallowing quantities of scum, or shoreline matter or crust or licking their coats that have been contaminated by the algae or toxins. Dogs have died after going into the water at the shores of affected lochs. If affected dogs (or other animals) can deteriorate very quickly and effects may occur after very little contact.

Canoeists, wind surfers and swimmers who have either swum through algal scum or swallowed it have suffered from skin rashes, eye irritation, vomiting, diarrhoea and pains in muscles and joints. Illnesses can be severe, particularly where affected water has been swallowed

What should I do about blue-green algae?

Be vigilant when using watercourses or shorelines.

When in doubt, stay out.

  1. Avoid all contact with the affected waters and ensure that children are kept away.
  2. Do not let your pets and other animals go into or drink the water or consume the scum
  3. Do not drink the water or use it for cooking
  4. Farmers should ensure that their animals do not have access to contaminated water. This may require fencing around suspect waters.
  5. If you must swim or enter the watercourse or loch, keep away from the algae and scum
  6. If you believe your pet may have been exposed to blue green algae then contact your vet as soon as possible to get advice.

If any member of the public finds areas of water they believe may be affected with blue-green algae , take a photo and report it on the Bloomin’ Algae website or app, and report it to the Councils environmental health at envhealth@argyll-bute,

What are the council doing?

The council cannot control or mitigate the occurrence of blue green algae in watercourse and lochs, as it is naturally occurring. Our aim is to raise awareness of the risk to allow members of the public to be aware of the likely presence of blue-green algae, and make informed choices about their own actions.

Risk assessments have been undertaken of waterbodies where blue-green algae has previously occurred and in areas of high risk, semi-permanent signage has been erected to inform and warn members of the public of potential risks and actions to be taken in the presence of algae. The sign is as follows.

Blue Green Algae Public Warning Notice
Blue Green Algae Temporary Warning Notice

Permanent signage is located at the following lochs. You are advised to be aware and vigilant about the likelihood of blue-green algae and follow appropriate advice when using the watercourse or shorelines. Please note that whilst the signage is located at various parts of the loch, the advice is pertinent across the whole loch or watercourse as the algae can be dispersed and move about the loch with weather and currents.

Loch Eck, Cowal


Grid Ref.

Lock Eck Holiday Lodges

NS 141 868

Loch Eck layby south of Inverchapel Lodge

NS 142 872


NS 142 879

Coylet Inn

NS 142 886

Loch Eck Caravan Park

NS 143 888

Layby 2

NS 139 908

Layby 3

NS 141 924

Rubha Croise car park (Jubilee Point)

NS 141 930

Whistlefield Inn

NS 143 933

Layby 4

NS 141 946

Loch Nell, by Oban


Grid Ref.

Lock Nell Pump House Gate 

NM 881 266

Lock Nell Bench

NM 881 271

Loch Awe, Argyll


Grid Ref.

Dalavich Café / Notice Board

NM 969 127

Dalavich Laundry

NM 970 128

Loch Awe Gate at Shore Walk

NM 998 175

Taychreggan Hotel

NN 047 214

Ardanaiseig Hotel

NN 088 248

Kilchurn Castle car park

NN 138 279

Kilchurn Castle viewpoint

NN 134 271

Loch Avich, Argyll


Grid Ref.

Loch Avich 1

NM 952 154

Loch Avich 2

NM 949 154

Loch Lomond

Tarbet Pier

Firkin Point

Luss Caravan and Camping site

Lodge on Loch Lomond

Luss beach

Duck Bay beach

Rossdhu South Gates

In lochs and waterbodies where there is no permanent signage, the Council will post our website and social media of any notifications or reports received  We will consider posting and will consider whether temporary warning notices are necessary, as blue-green algae blooms can be short-lived, transient and may move around a body of water due to weather conditions.

What about eating fish from affected waters?

Blue-green algae and their toxins can adversely affect fish growth and health and, in some circumstances, can cause fish kills.

Fish should not be consumed if dead fish or strange fish behaviour is seen, blue-green algal scum is present or notices are displayed indicating the presence of blue-green algal cell numbers or toxins in unsafe levels.

Anglers and pet owners should not feed the liver or guts from fish to their pets, when fish are caught in waters affected by blue-green algae, as described above.

If you would like any further advice about blue-green algae, please contact your local environmental health service or call 01546 605519.

Other invasive or harmful plants

You can find out information about other invasive or potentially harmful plants in Argyll in the invasive and harmful plants section.

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