Blue-Green Algae Poisoning in Pets UK — Dogs & Cats Emergency

According to the BVA, blue-green algae are microscopic bacteria called cyanobacteria that multiply in warm, nutrient-rich stagnant water. They are not true algae but produce some of the most dangerous natural toxins affecting UK pets.

In summer and early autumn — typically May to September — UK lakes, ponds, gravel pits, canals, and slow-moving rivers can develop blooms. Climate change and agricultural runoff have increased bloom frequency across Britain.

Cyanobacteria release toxins that damage:

• Liver — acute liver failure
• Nervous system — tremors, seizures, paralysis
• Skin — irritation from direct contact

Dogs are the most common UK victims because they swim, paddle, and drink from water during walks. Cats that drink from garden ponds or groom after wetland exposure are also at risk.

Poisoning occurs when pets:

• Drink contaminated water
• Swim or paddle and swallow water while playing
• Lick wet fur after swimming in toxic water
• Eat dried algae scum on shorelines — toxins remain when blooms dry

Even small amounts of highly toxic blooms can kill a dog. There is no safe exposure level when concentrations are high.

According to the PDSA, deaths occur every summer when owners assume a familiar pond is safe because it was fine last year. Blooms appear suddenly and can clear within days — risk changes daily.

The BVA warns that algae may not always be visible. When present, warning signs include:

• Green, blue-green, or brown scum on the water surface
• Pea soup appearance — uniform green colour
• Foam along the shoreline
• Dead fish or waterfowl in or near the water
• Musty or sewage-like smell (not always present)

Many UK local authorities post algae warnings at popular lakes and reservoirs. Heed signs and report new blooms to the Environment Agency via their incident hotline.

Signs may appear within 15 minutes to a few hours — sometimes delayed up to 24 hours for liver toxins.

Acute neurological signs

• Vomiting and diarrhoea
• Drooling and retching
• Muscle tremors and rigidity
• Seizures
• Collapse and paralysis
• Sudden death — sometimes before other signs are noticed

Liver failure signs

• Vomiting and diarrhoea (may be bloody)
• Weakness and lethargy
• Jaundice — yellow gums or skin
• Bleeding — nosebleeds or bloody stools
• Swollen abdomen

Cats may show similar signs but are less likely to swim. Outdoor cats drinking from garden water features need the same seasonal caution.

Do not wait for symptoms — prevent exposure is the only reliable protection.

• Keep dogs on a lead near stagnant water in summer — especially after heatwaves
• Carry fresh drinking water and a collapsible bowl
• Avoid throwing toys into unknown lakes or ponds
• Check garden ponds — small features bloom quickly in heat; consider netting or removing standing water
• Rinse after sea swimming too — salt water is different but carries separate risks; fresh stagnant water is the algae threat
• Plan walks during hot weather pet safety with water awareness

Working breeds and puppies are often enthusiastic swimmers — train alternative play on dry land near water.

Not all open water carries algae risk. Flowing rivers with clear current are generally lower risk than stagnant ponds. Designated bathing waters monitored by councils are safer than isolated gravel pits.

However, the BVA position is clear: if you cannot confirm safety, keep pets away. The consequences of one drink are catastrophic.

Saltwater swimming at the beach does not carry cyanobacteria risk from algae blooms — but tides, currents, and heat exhaustion remain concerns. See can I walk my dog in hot weather UK.

Report suspected blue-green algae blooms to:

• Environment Agency — 0800 80 70 60 (UK pollution hotline)
• Local council — for parks and public lakes
• Canal and River Trust — for canal networks

Public reporting helps authorities post warnings and reduces further pet and wildlife deaths.

Outdoor cats accessing neighbour ponds or water troughs face lower but real risk. Bird baths and small garden features can bloom in heatwaves — refresh water frequently.

Wild birds and fish die during blooms — finding dead wildlife near water is a warning sign to keep all pets away.