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Blue-Green Algae: A Deadly Threat In Plain Sight

May 15, 2025

Cyanobacteria, or blue-green algae, flourishes in warm water. It produces a toxin that is harmful—and potentially fatal—to both humans and animals. All pet owners should be aware of this, but it is especially critical for those who take their canine companions swimming in fresh water. Continue reading for more information on this hazard from a local Mattoon, IL veterinarian.

What is Blue-Green Algae?

Cyanobacteria is a type of algae that is especially harmful because it produces a specific toxin. It is typically found in shallower lakes and ponds. Blooms can occur whenever the average water temperature rises over 75 degrees Fahrenheit, which is when many bodies of water are nutrient-rich. That means that the time when temperatures peak—particularly around and soon after the hottest days of summer—is especially risky. When conditions are favorable, blooms can expand rapidly.

How Can I Tell If Blue-Green Algae Are Present?

Algae blooms that are blue-green in color are typically quite simple to identify… and smell. Cyanobacteria is referred to as blue-green algae for good reason. The blossoms resemble pea soup or green paint. They frequently emit a smelly, marshy odor.

However, you cannot rely solely on appearances. Smaller blooms may be difficult to detect with the naked eye.

Blue-Green Algae Blooms: How Dangerous Are They?

Blue-green algae is extremely harmful to humans and animals. Diarrhea, nausea, vomiting, skin rashes, eye and throat irritation, and respiratory distress are all possible side effects of exposure. It may also result in major brain issues and/or liver failure. Large concentrations of algae can be deadly. Unfortunately, there is no remedy.

Dogs and animals are especially vulnerable because they know no better than to drink the water and can consume a large amount before being stopped.

Is Blue-Green Algae Ever Safe to Swim in?

Absolutely not. Part of the risk is that blooms may be there but undetectable. Even if a lake or pond appears to be safe, conduct your own research and check local resources. Stick to areas that have been cleared for swimming.

What Are the Signs of Exposure in Dogs?

It is always crucial to keep an eye on your pet and look for signals of trouble. In this situation, look for panting, respiratory issues, vomiting, diarrhea, dizziness/disorientation, and excessive drooling. Seizures are another cause for concern. If you see any of these symptoms in your canine companion, contact your veterinarian or an urgent care pet facility right away.

As stated before, there is no antidote. However, receiving good supportive care can make a significant difference. For more information, consult with your veterinarian.

How Does One Get Contaminated By Blue-Green Algae?

Drinking contaminated water is perhaps the most common cause of illness in dogs, but it is not the only one. Toxins can also be ingested by humans and pets through their skin or by breathing in water droplets or mist. Tubing, water skiing, swimming, floating, or boating can all expose you to contamination. Dogs may also lick the cyanobacteria off of their fur.

It’s worth noting that cats are usually less susceptible, simply because most of them hate water. However, Fluffy could still try to drink from a contaminated source. Err on the side of caution and keep your feline friend safe and sound inside.

How Can I Tell if a Lake Is Safe for Fido?

If you smell a swamp odor or detect the unmistakable green scum, assume the lake is hazardous. However, as previously indicated, the bloom may not be seen. Look for public signs: many local governments will publish notices after blooms have been confirmed.

You can also look at the HAB (Harmful Algae Blooms) map, which can be found here. This website provides blue-green algae bloom updates for each state.

What Should I Do if My Pet Comes into Contact With Cyanobacteria?

Your first step should be to thoroughly wash Fido. We would strongly suggest you call your veterinarian as well. You may find yourself in a waiting game as you look for any warning indicators. Or, you may be advised to go to a pet urgent care center immediately.

How Long Do Blue-Green Algae Blooms Last?

Individual blooms only endure for one or two weeks. When conditions are favorable, they can be quickly replaced by another. Lakes can remain poisoned for weeks or even months. This normally takes place between mid-to-late summer and early autumn.

Will Boiling Water Eliminate Blue-Green Algae?

No. This is vital to remember if you enjoy going camping with Fido and frequently boil water from lakes or ponds, and then use it for drinking, bathing, or cooking. While boiling can kill live bacteria and microorganisms, it does not remove cyanobacterial toxins.

What Else Can I Do to Keep Fido Safe at the Lake?

Cyanobacteria aren’t the only potential threat at lakes. Fido can have a lot of fun swimming, but it can also be dangerous. Some canines are just not made out for it. If your pup is brachycephalic or has mobility limitations, he’ll do better in a kiddie pool. Very tiny dogs are also unsafe in the water since they can get above their heads in a matter of inches. If you’re unsure whether swimming is safe for Fido, see your Mattoon, IL, veterinarian.

If your canine companion does not know how to swim, make time to teach him. Never simply throw a puppy in the water and hope for the best. Encourage him while he is learning by giving him praise and comments.

However, it is critical to keep an eye on Fido while he is in the water. Never leave your dog unsupervised near water. You’ll want to avoid taking him someplace that has blue-green algae blooms, as well as steep drops, large wakes, or strong currents. Red tides are also a concern for people planning a summer trip to the beach.

Your canine companion should also be familiar with basic obedience instructions like Sit, Stay, and Come. This is crucial, as it can prevent your pup from approaching a hazardous area. If you’re taking your dog to a pool, take the time to teach him where the stairs are.

Regardless of whether Fido was swimming in a pool, lake, or on the beach, we always recommend rinsing him off. It’s always best to remove sand, salt, and/or chemicals from his fur and skin. (Be sure to give him a treat after!)

Finally, never allow Fido to drink from lakes, ponds, or puddles. Fido is at risk of contracting parasites like Giardia in addition to cyanobacteria. Ask your vet for more information. 

Conclusion: Blue-green algae (cyanobacteria) is a harmful algae that grows in many lakes and ponds during the summer. It is exceedingly hazardous to both pets and cattle. In fact, it can be lethal for our canine companions. Pet owners must understand the risks and how to recognize and avoid blooms.

Make An Appointment With Your Mattoon, IL Pet Hospital

Is it time for Fido to have a checkup? Is he in need of wellness care, vaccinations, or parasite control? Please contact your local Mattoon, IL animal clinic at any time.

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