It started out as a regular romp around the reservoir in Derbyshire, England with her 4-month-old yellow lab. The puppy, named Ted, had been “messing about around the beach area and nibbling on something,” Ted’s owner Kate Sealy told a British newspaper. Shortly after they arrived home the dog started to vomit. Sealy took him to the vet, but he died.

Blood tests confirmed that blue-green algae had killed Ted. "I knew nothing about this algae at all,” Sealy said, “and I don't want anyone else's dog… to suffer like Ted."

Blue-green algae is the name for many different species of microscopic bacteria, called cyanobacteria, that synthesize food from water and sunlight. With the advent of of global warming, it’s increasing common in lakes, ponds, rivers and ocean water. When these algae overgrow into blooms, they can produce toxins that can sicken and even kill dogs, according to the ocean education group Sea Grant New York.

Related: 10 Foods You Should Never Feed Your Dog

The blooms occur in all 50 states, according to the U.S. Environmental Protection Agency. They are most likely to appear in summer and fall or when water temperatures are between 60 and 86 degrees Fahrenheit. In addition, storm water runoff can wash nutrients into lakes or ponds, fueling blooms.

A 2013 article in the journal Toxins found 368 cases of blue-green algae cyanotoxin poisoning among dogs in the United States from the late 1920s to 2012 (which is likely only a small fraction of cases, the researchers noted). More than 200 fatalities were reported among breeds from small terriers, pit bulls and mutts to water-loving dogs like retrievers.

Dogs are most likely to get poisoned by a blue-green algae bloom while “swimming, drinking the water when swimming and grooming themselves afterwards,” says Barry N. Kellogg, DVM, senior veterinary adviser of the Humane Society of the United States.

Signs of blue-green algae poisoning

In dogs, toxins produced by cyanobacteriacan lead to liver problems or attack the nervous system and skin.

Signs of blue-green algae poisoning include:

  • vomiting
  • diarrhea
  • weakness
  • lethargy
  • staggering
  • difficulty breathing
  • black, tarry stools
  • excessive drooling
  • pale mucous membranes
  • seizures
  • muscle tremors or rigidity
  • coma

In severe cases, liver and nerve toxins can kill animals within an hour of exposure, according to Sea Grant. Although there are no known antidotes to cyanobacteria poisoning, rush your dog to the vet immediately if you suspect poisoning.

Blue-green algae can sicken people as well, so don’t play or swim in lakes or other bodies of water that look green or foamy.

Related: When to Take a Sick Pet to the Vet

Protecting your pooch

Harmful algae blooms often look like spilled paint or pea soup, but they can also look like scum, foam or floating mats, according to Sea Grant New York. Problematic algae are usually green to blue-green in color, but at the end of a bloom they can also look red, brown or even white. The scum or mats can wash up on shore, where pets may grab a mouthful. Unlike humans, dogs enjoy the smell of the scum, Sea Grant says.

“Not all blooms produce toxins,” Kellogg says. “However, you can’t tell by looking at it, so all blooms should be considered toxic.” The bottom line: Keep your dog out of any lakes, ponds or other water that looks green or contains algae.

Sea Grant New York offers these additional tips to protect your pet:

  • Keep your dog leashed near shorelines.
  • Don’t let dogs wade in or drink the water or nibble on or walk in shoreline debris.
  • If your dog goes in suspectwater, remove him immediately.
  • Don’t let him lick his fur or paws when he gets out of the water.
  • Rinse or wash himwith fresh water from a safe source; use rubber gloves during cleaning if possible. You can use a towel or rag to remove algae.
  • Dry your pet thoroughly with a clean towel or rag; wash your hands with fresh water afterward.
  • Keep a close watch for possible symptoms of poisoning.

Report suspected algae blooms to your state department of health or environment. To find resources in your state, go to the EPA website state resources page and click on your state.

Related: 13 Health Symptoms Dog Owners Should Never Ignore

Kathleen Carlson is a Nashville freelance journalist. She has written for The Tennessean, Nashville Banner, Nashville Ledger and other publications, covering business, crime and courts, workplace issues, general assignment and features. In addition, she has written specialty publications for human resources managers, copy edited at two daily newspapers and edited a small newspaper for a Middle Tennessee religious community. Her favorite safety suggestion is to use sunscreen every day.