The sun is shining, temperatures are rising, and the water is calling. For many dog owners, a swim in the lake or pond is part of the perfect summer day. But what if that refreshing dip hides a dangerous secret? Blue-green algae—also known as cyanobacteria—are an increasing threat in the Netherlands each summer. Often invisible to the naked eye, they can be deadly for dogs.
At YMOAs, our mission is to help you enjoy quality time with your dog safely, all year round. In this article, we explain what blue algae are, why they're dangerous, where they appear, and most importantly, how to avoid them.
What Are Blue-Green Algae?
Blue-green algae are not true algae but bacteria that thrive in stagnant, nutrient-rich freshwater. Under warm conditions and with nutrients like phosphates from agriculture, they bloom rapidly, known as an "algal bloom." Sometimes, a green or bluish film appears on the surface, but often the water looks perfectly clear (RIVM, 2024).
Some species produce cyanotoxins, such as microcystins (which damage the liver) and anatoxins (which attack the nervous system). Since dogs tend to drink water or lick their fur after swimming, they are at heightened risk (Utrecht University, 2023).
Why Are Blue Algae So Dangerous for Dogs?
Unlike humans, who may experience only skin irritation, dogs can become seriously ill—even fatally so—from small amounts of contaminated water. Cyanotoxins act fast. Symptoms may appear within 15 minutes, and a dog’s condition can deteriorate rapidly without treatment (NVWA, 2023).
Symptoms of Blue Algae Poisoning in Dogs
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Vomiting and diarrhea (sometimes bloody)
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Lethargy or muscle tremors
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Difficulty breathing
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Excessive drooling
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Seizures or twitching
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Loss of coordination or paralysis
In severe cases, dogs may die within hours due to liver or respiratory failure (British Veterinary Association [BVA], 2022).
Where Does Blue Algae Occur in the Netherlands?
Blue algae thrive in stagnant or slow-moving water such as recreational lakes, canals, ponds, and reservoirs. In hot summers, many water bodies across the Netherlands are affected. Risk areas include:
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Vinkeveense Plassen
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Loosdrechtse Plassen
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Wolderwijd
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Parts of De Biesbosch
Recent Warnings:
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July 17, 2025: Water board Aa en Maas issued warnings for canals due to low water levels
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July 17, 2025: Municipality of Teylingen banned swimming at 't Joppe (Kagerplassen)
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July 15, 2025: Blue algae found in De Dobbe, Zwolle; pet warning issued
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July 17, 2025: Blue algae detected in multiple waters in Zeeland; pet warnings shared
How Are Blue Algae Warnings Issued?
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Physical signs near water sites
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Real-time alerts via www.zwemwater.nl
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Weather and water quality apps (like Buienradar)
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Local government and water board updates
🗺️ Blue-Green Algae Alerts in the Netherlands: Where to Check for Local Risks
Planning a water day with your dog? Be sure to check whether your favorite swimming spot is safe. In the Netherlands, several trusted sources provide real-time blue-green algae alerts:
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Zwemindex.nl - Blue Algae Radar: This interactive map shows up-to-date blue-green algae reports at over 80 locations nationwide. Search by postal code or region to see nearby risks.
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Zwemwater.nl (Rijkswaterstaat): The official government site for checking water quality, algae alerts, and swimming bans at recreational sites across the country.
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Waterschap Aa en Maas and Waterschap Brabantse Delta also publish local alerts and provide interactive maps showing where blooms have been confirmed.
You can also receive alerts through weather apps (like Buienradar) or subscribe to updates from your municipality or local water board. If you see suspected blue algae, report it via the swimwater website and warn other dog owners.
How to Recognize Contaminated Water
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Floating green-blue or oily film
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Foul smell (like rotting fish or soil)
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Dead fish or birds nearby
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Warning signs posted by local authorities
⚠️ Important: Not all contaminated water looks dangerous. When in doubt, stay out.
What to Do If Your Dog Was Exposed
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Rinse your dog immediately with clean tap water
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Prevent licking of fur
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Closely monitor your dog for symptoms
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Contact your vet immediately if symptoms appear
⚠️ There is no antidote for cyanotoxins. Treatment is supportive (fluids, seizure medication, respiratory aid). Fast action can save lives (Diergezondheidscentrum Zuid-Holland, 2023).
Prevention Tips: Safe Summer Swimming
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Check www.zwemwater.nl for official warnings
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Avoid stagnant, green, or foul-smelling water
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Always bring clean drinking water and a collapsible bowl
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Rinse your dog after swimming
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Keep dogs leashed in high-risk areas
👉 Related Reading: Beach & Pool Safety Tips for Dogs
What Can You Do if You Spot Blue Algae?
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Avoid the area and warn other dog owners
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Report it to the water board or via www.zwemwater.nl
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Share updates in local apps or online groups
Closing: A Safer Summer Together
Blue algae are summer killers in disguise. Don’t be fooled by clear water or busy beaches. Protect your dog by staying alert, taking preventive steps, and spreading awareness.
Want more water safety tips? Read our Beach & Pool Safety Guide for Dogs or subscribe to our newsletter for seasonal updates.
References (APA 7th Edition)
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British Veterinary Association. (2022). Blue-green algae: Deadly danger for dogs. https://www.bva.co.uk
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Utrecht University Faculty of Veterinary Medicine. (2023). Blauwalgen bij huisdieren: Herkenning en preventie.
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Diergezondheidscentrum Zuid-Holland. (2023). Emergency care for blue algae poisoning.
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NVWA – Dutch Food and Consumer Product Safety Authority. (2023). Blue algae and animal health.
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RIVM – National Institute for Public Health and the Environment. (2024). Blue algae in recreational waters. https://www.rivm.nl/blauwalgen
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Rijkswaterstaat. (2024). Zwemwater.nl – Swimming water safety. https://www.zwemwater.nl
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Waterschap Aa en Maas. (2025, July 17). Low water levels and blue algae warnings. https://www.aaenmaas.nl
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Municipality of Teylingen. (2025, July 17). Swimming ban at 't Joppe due to blue algae. https://www.teylingen.nl
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NH Nieuws. (2025, July 15). Blue algae found in Zwolle pond – dogs must stay away. https://www.nhnieuws.nl
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HV Zeeland. (2025, July 17). Blue algae detected in surface waters in Zeeland. https://www.hvzeeland.nl