Toxic algae in a popular Snowdonia lake has prompted a warning to visitors and dog walkers.
The harmful blue-green algae (BGA) has been spotted on the banks of Wales’ largest lake, Llyn Tegid in Bala, Gwynedd.
Eyri National Park authorities urged visitors on its social media channels to be careful when visiting the lake - which is a popular location for anglers, kayakers, bathers and paddleboarders.
The substance can be fatal for animals who come into contact with it and it can also be harmful to humans - causing skin and stomach problems or more serious illness.
They said: “IMPORTANT WARNING: Blue-green algae has been seen in parts of Lyn Tegid, Y Bala.
“This can be a natural event in the summer under different circumstances. Be careful around the lake and don’t come across the algae.
“If you intend to visit Lake Tegid, remember to read the safety information on the information boards around the lake.”
Also known as cyanobacteria, blue-green algae can appear in lakes and reservoirs during hot weather and produce toxins when it clumps together in larger blooms.
Scientists confirmed the first conclusive dog death caused by the algae in the last few weeks, when a two-year-old retriever died 45 minutes after ingesting algae during a walk at Wimbleball Lake in Exmoor National Park.
The Canal and River Trust said: “When BGA grows excessively and reaches the stage of producing scum on the water’s surface, it can sometimes produce toxins. This causes a problem if animals drink the water. There have been some cases of dogs and cattle dying or developing long-term health problems because they’ve ingested BGA.
“These toxins will affect humans too if we accidentally consume them after putting our hands in the water or swimming. They can cause skin and stomach problems, as well as more serious illnesses. Children are more at risk than adults.
“Large amounts of BGA can also use up a lot of the oxygen in the water overnight. This can drastically reduce the amount of oxygen available for fish and other aquatic creatures, which sometimes kills them.”