Water hazards for dogs: These 7 things could harm Spot. Flesh-eating bacteria isn't one.

Costa, a 4-year-old golden retriever, looks and acts like an old dog.

Last September, Costa nearly died from eating a clump of toxic blue-green algae behind the house she shares with her owners, Adam and Ashley Guzi, on the St. Lucie River near Stuart. 

"She's lucky to be alive," Ashley Guzi said, "but she hasn't been the same. She wears herself out quickly; her face has turned white, like an old dog's. Before the algae, she was still in her puppy phase; but now she acts like a senior dog."

Costa survived because Guzi took her quickly to a veterinarian who recognized the symptoms of an encounter with toxic algae.

Water hazards for pets

Blue-green algae isn't the only potential toxic threat to your pets in Florida waters. Other algae and bacteria known to make people sick, or even be fatal, can harm pets, too.

"The rule of thumb is that all toxins work the same, whether in humans or in animals," said Dr. Cristina Maldonado, a Stuart veterinarian. "It's just that the effects will be different."

Symptoms, particularly lethargy, vomiting and diarrhea, can begin within 30 minutes of contact with a toxin.

"If you see symptoms and know, or even suspect, that your pet has been in contaminated water, get them to a vet immediately," Maldonado said.

Here's a look at some of the organisms in Florida waters and how they can affect your pets. The focus is on dogs because they're the most likely to get in the water.

Blue-green algae

The toxic blue-green algae in the St. Lucie River in 2018 that nearly killed Costa did kill Finn, a healthy 9-year-old standard poodle owned by Misty Aydelotte of the Rio community, and made at least four other dogs sick.

More: Necropsy shows toxic algae in St. Lucie River killed dog

A necropsy found Finn died of "acute toxicity due to ingestion of blue-green algae (cyanobacteria) toxins."

All the dogs had been in contact with the algae-laden water; Finn and some of the others ate dead fish covered with algae.

All the dogs suffered serious liver damage and had internal bleeding. Most received plasma transfusions to help their blood clot so they wouldn't bleed to death.

"If you live on the river or go to the river, and there's algae in the water, don't let your dog off leash," Maldonado said.

Red tide

It stands to reason the red tide that killed millions of fish on Florida's east and west  coasts as well as hundreds of sea turtles, dozens of manatees and dolphins and even a whale shark on the Gulf Coast in 2018 would harm your pets as well.

Red tide produces toxins that affect the nervous systems of fish and other marine animals. Larger marine mammals can die by eating infected fish. It can also kill sea birds by producing a foam that removes the waterproofing on their feathers.

Just breathing around red tide can cause coughing and sneezing in humans; swimming in it can cause skin and eye irritation.

More: You don't have to go to beach to feel red tide effects

Dogs tend to lick themselves when they're wet and can ingest toxins from red tide from their fur. If your dog swims in or around a red tide bloom, wash it as soon as possible and keep an eye out for symptoms.

Enteric bacteria

A sign of fecal contamination, enteric bacteria typically gets in waterways when heavy rains — like those in the area since Sunday — wash feces from pets, livestock and wildlife into the water.

Potential health risks for those who ingest or come in contact with the water include upset stomach, diarrhea, eye irritation and skin rashes.

"The problem with enteric bacteria is that, unlike blue-green algae, you can't see it in the water," Maldonado said. "Heed the warnings that the health department puts out about high bacterial levels, and keep your pets out of those areas."

Vibrio vulnificus

Vibrio vulnificus — a naturally occurring bacteria found mostly in warm, slightly salty water in coastal estuaries — infected 397 people in Florida since 2008, killing 108 of them.

The bacteria usually enter the body through a cut or abrasion. Eating raw seafood, especially oysters, from contaminated water is also a common cause of infection.

The good news: "Dogs can't get vibrio," Maldonado said. 

More: Vibrio bacteria killed PSL man via fin prick while fishing in Indian River Lagoon

Pseudo-nitzschia

An algaelike organism called Pseudo-nitzschia, which produces a toxin known to kill animals, including humans, and cause seizures and erratic behavior, has been found in very low levels in Indian River Lagoon water and in fish caught in the lagoon.

The toxin, domoic acid, has not been linked to any deaths or illnesses along the lagoon, said Malcolm McFarland, a Harbor Branch research associate.

The toxin can cause similar symptoms in dogs, Maldonado said, "but it doesn't appear to be in quantities in Florida that are enough to affect them — yet. It's something we need to keep an eye on."

Lyngbya

Another blue-green algae found in the Indian River Lagoon, lyngbya often looks like masses of brown seaweed floating on the water, especially in the summer.

Lyngbya (LING-bee-yah) can be toxic to fish, plants and other marine creatures and cause a skin irritation known as “swimmer’s itch" in humans.

It grows rapidly in water with high levels of fertilizer and septic runoff, so blooms are a sign of an unhealthy lagoon.

Contact with lyngbya toxins can give humans itchy rashes and skin lesions. Animals that drink water with lyngbya can can get irritated mouths and intestines, swelling and cell damage.

Lyngbya has been known to kill horses that ate the bloom material after it washed ashore.

Sargassum seaweed

The seaweed with small air-filled "berries" that floats in islandlike masses on the ocean and piles up on Florida beaches can contain arsenic and heavy metals (so son't eat it) and emits hydrogen sulfide as it rots.

More: Sargassum seaweed contains arsenic, heavy metals, emits 'rotten egg' smell

Breathing hydrogen sulfide can irritate the eyes, nose and throat. At higher levels typically not found in beach encounters, the chemical can cause headaches, poor memory, tiredness and balance problems.

Sargassum isn't toxic to touch, but touching some of the organisms living in it, such as jellyfish larvae, can cause skin rashes or blisters.

As with humans, sargassum tends to be more of an irritant than a health threat for dogs, Maldonado said.

Seawater itself

That's right: Clean ocean water can cause problems for Fido — if he drinks enough of it.

Drinking salty water can cause your dog to dehydrate, which can make them drink more ocean water. Vomiting and diarrhea can result.

Most dogs learn not to drink ocean water after one or two visits to the beach, but there can be serious problems in those first visits.

"Take you dog to the beach in the early morning or evening," Maldonado said, and bring along lots of fresh water. "A hot day on the hot sand with no fresh water, and they can become severely dehydrated."