Surprise as algae slicks 'like green paint' appear at popular Eryri lake

Andrew Forgrave
·2-min read
Bright green blooms on the edge of the lake
-Credit: (Image: Lilian Stokes)


Visitors at a popular Eryri lake have been alarmed by the apparent appearance of “paint slicks” on its surface. Blue-green algae was suspected and the National Park Authority (NPA) has since confirmed its presence at Llyn Tegid, Bala.

Blooms of the harmful algae are not uncommon on the lake but usually they are in summer as the water warms. Its appearance in November has shocked regular visitors who thought the danger had passed, prompting speculation of a link with climate change. “It looks like someone’s chucked in a load of lime green paint,” said one woman.

When blue-green algae is present, Eryri NPA warns people to be careful as its toxic to humans and animals, either through skin contact or ingestion. Dogs and livestock are especially vulnerable and they can quickly become severely ill or die.

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The authority said winter blooms were “surprising” and blamed recent weather. Wind-created waves will disperse the algae but a fortnight of calm conditions has enabled it to gather in slicks on the shoreline.

A NPA spokesperson said: “Although rare, it’s not unusual for blue-green algae to appear at this time of year. Currently, the presence of algae in Llyn Tegid is due to the still, settled weather we’re experiencing for the season, which has allowed the algae to pool at the lake’s edges.

“It’s worth noting that we also recorded blue-green algae in Llyn Tegid last year on November 1. So while its appearance in late autumn may be surprising, it is not unprecedented.”

NPA wardens monitor the lake for algae and this summer a series of warning signs were erected when blooms were spotted. These have yet to be removed, said the authority, and the safety alert remains in place. Join the North Wales Live WhatsApp community group where you can get the latest stories delivered straight to your phone

Sections of the shoreline have turned green
Sections of the shoreline have turned green -Credit:Lilian Stokes

In June, a dog owner warned others to be vigilant after her pet almost died after visiting the lake. Only prompt action saved the dog’s life - you can read about this here.

Llyn Tegid is a popular watersports venue and people who come into contact with blue-green algae can suffer skin rashes, vomiting, diarrhoea and fever. If blooms are present, even if just on the shoreline, Eryri NPA advises users to “err on the side of caution”.

It suggests people refrain from entering the water as algae toxins can be dispersed throughout the lake. Get all the latest Gwynedd news by signing up to our newsletter - sent every Tuesday

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