Warm weekends often mean lake days, park walks, backyard play, and quick trips around St. Peters, O’Fallon, St. Charles, Cottleville, Wentzville, and Lake St. Louis. For many dogs, water is part of the fun. However, some lakes, ponds, creeks, and slow-moving waterways can become dangerous during hot weather, especially when blue-green algae is present.

Blue-green algae, also called cyanobacteria, can produce toxins that may make pets seriously ill. In some cases, exposure can become an urgent veterinary situation very quickly. That is why knowing what to avoid, what symptoms to watch for, and when to seek help can make a meaningful difference.

What Is Blue-Green Algae?

Blue-green algae is not always obvious at first glance. It may look like thick green paint, foam, scum, or mats floating on the surface of the water. Sometimes the water may appear bright green, blue-green, white, red, yellow-brown, or cloudy. It may also smell unpleasant, especially as the bloom begins to break down.

These blooms are more common during warm weather, particularly in still or slow-moving water. Around St. Charles County, that can include ponds, lakes, creeks, and other waterways where pets may be tempted to swim or drink.

For local guidance on this issue, St. Charles County provides information about harmful algal blooms and how they may affect people, pets, and animals in the area.

Why Lake Water Can Be Risky for Dogs and Cats

Dogs are often at higher risk because they may drink from lakes, retrieve toys from the water, lick wet fur, or chew on algae-covered sticks. Cats may be less likely to swim, but outdoor cats can still be exposed near ponds, drainage areas, or contaminated water sources.

Pets can become sick after:

• Drinking contaminated water
• Swimming in water with harmful algae
• Licking algae or toxins from their coat
• Eating contaminated fish or shoreline debris
• Inhaling tiny water droplets during play

Unfortunately, harmful algal toxins can affect the liver, nervous system, skin, stomach, and respiratory system. Because symptoms may progress quickly, it is safest to treat suspected exposure as urgent.

The CDC explains how animals may be exposed and how pet owners can reduce risk in its guide to preventing pet and livestock illnesses caused by harmful algal blooms.

Warning Signs After Water Exposure

If your pet recently played near a lake, pond, creek, or slow-moving water, keep a close eye on their behavior afterward. Symptoms may appear soon after exposure, though timing can vary depending on the toxin and the amount involved.

Signs that should never be ignored include:

• Repeated vomiting or diarrhea
• Drooling or foaming at the mouth
• Weakness, collapse, or sudden lethargy
• Difficulty breathing
• Tremors, seizures, or disorientation
• Pale, blue, or abnormal gum color
• Excessive panting unrelated to heat
• Sudden unexplained behavioral changes
• Crying out in pain or severe distress

Additionally, skin irritation, eye redness, or itchiness may occur after contact with contaminated water. Even if your pet seems “mostly okay,” symptoms can worsen, so it is better to call a veterinarian sooner rather than later.

For more details about illness signs linked to freshwater blooms, the CDC offers an overview of symptoms caused by freshwater harmful algal blooms.

What to Do Right Away if You Suspect Exposure

If your pet may have been exposed to blue-green algae, act quickly but stay calm.

1. Remove your pet from the water immediately.
2. Prevent them from licking their fur, paws, collar, leash, or wet gear.
3. Rinse your pet with clean tap water if you can do so safely.
4. Wear gloves or wash your hands thoroughly after handling your pet.
5. Do not let your pet drink more lake or pond water.
6. Call a veterinary team and explain where your pet was, what the water looked like, and what symptoms you are seeing.

Also, avoid giving home remedies unless a veterinarian specifically instructs you to do so. In particular, do not try to induce vomiting without professional guidance.

If your pet is vomiting repeatedly, weak, having trouble breathing, trembling, collapsing, or acting disoriented, seek urgent care immediately. Pet Urgent Care of St. Peters provides emergency and urgent care for dogs and cats when sudden symptoms need prompt attention.

The CDC also shares practical safety steps for pet owners in its resource on how to keep pets safe near lakes and rivers.

When to Visit Pet Urgent Care of St. Peters

Blue-green algae exposure can be frightening because there is no reliable way to tell how dangerous a bloom is just by looking at it. Moreover, pets can decline rapidly after swallowing toxins.

Bring your dog or cat to Pet Urgent Care of St. Peters right away if they show signs such as repeated vomiting or diarrhea, breathing difficulties, collapse, seizures, weakness, or sudden behavior changes after being near suspicious water.

Our facility bridges the gap between your regular veterinarian and a full emergency hospital. We welcome walk-ins for urgent and emergency care, and we ask that you call to let us know you are on your way so our team can prepare for your pet’s arrival.

Because every second counts, your pet will be seen within a maximum of 10 minutes after arrival. Our veterinarians can perform a prompt physical exam and use in-house diagnostics to assess your pet’s condition quickly. These tools may include bloodwork, electrolyte assessments, urinalysis, and other testing when appropriate. Fast results help guide faster treatment decisions when time matters most.

For veterinary-focused information, the American Veterinary Medical Association provides an animal health resource on harmful algal blooms.

How to Help Prevent Blue-Green Algae Exposure

The safest approach is simple: when in doubt, keep your pet out.

Before allowing your dog near a lake, pond, or creek, look carefully at the water. Avoid any area that appears discolored, has surface scum, looks like spilled paint, smells bad, or has dead fish nearby. Also, follow posted advisories from local or state agencies.

During summer outings, bring your own fresh water and a collapsible bowl. This helps reduce the chance that your pet will drink from unsafe water. After walks near lakes or creeks, wipe your pet’s paws and check their coat before they start licking themselves.

It also helps to keep dogs leashed near unfamiliar water. Even strong swimmers can get into trouble if they enter contaminated areas, swallow water, or come into contact with hidden debris.

For Missouri-specific information about animal safety and water toxins, visit the Missouri Department of Natural Resources page on harmful algal blooms and animal health.

Summer should be full of good memories, not unexpected veterinary emergencies. Still, lake and pond water can carry risks that are easy to overlook, especially during hot months in St. Peters and nearby communities.

If your pet becomes sick after swimming, drinking from a lake or pond, or walking near suspicious water, do not wait to see if symptoms pass. Pet Urgent Care of St. Peters is here to provide prompt, compassionate care when your dog or cat needs help quickly.

We are located at 5913 Mexico Rd, St. Peters, MO 63376, and we serve pets from St. Peters, O’Fallon, St. Charles, Cottleville, Wentzville, Lake St. Louis, and surrounding areas. Walk-ins are welcome, but please call ahead when possible so our team can prepare for your arrival.