>is it something that is visible ? if so what should I look out for ?
"
Blue green algae (Cyanobacteria) form in shallow, warm, slow-moving or still water, like ponds, lakes and some streams, particularly in summer. Despite their name, their colour ranges from olive-green to red. About 50% of these algae are harmless - some are actually used as health supplements. However, some produce toxins, which can be harmful to animals and humans. These can affect the skin (causing rashes and infections), the nervous system, or the liver, as in your dog's case. Signs of poisoning in dogs include fever, sickness, diarrhoea and loss of appetite. The effects vary from a mild skin infection to a fatal liver infection. The main problem is detecting the presence of blue green algae. Some susceptible areas have warning signs but the algae can occur anywhere, and their formation is unpredictable - the water may be clear one day and affected the next. The algae can be visible as surface scum but sometimes form deeper down and cannot be seen. The World Health Organisation has established guidelines on adverse effects in humans and some authorities have their own guidelines, including regular monitoring, discouraging human bathing and using signs. If you suspect a problem, contact the local water authority. Avoiding ponds and lakes during hot weather reduces the risk. However, as your case so tragically highlights, this can be a fatal, invisible problem. The safest option is to avoid still water"
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