In this guide
Yes, some algae are good for dogs, and some can kill a dog within hours. The safe kind is farmed microalgae sold as a supplement, mainly spirulina, chlorella, Nannochloropsis and the algae used to make algae oil. The dangerous kind is the blue-green algae that blooms on warm, still lakes and ponds.
If your dog has swum in or drunk from water with a green scum on it and is now vomiting, drooling, wobbly or weak, stop reading and phone your vet now. If you're here about supplements, this page explains what each alga does, how it differs from seaweed, how much to give and who should ask a vet first.
Blue-green algae in ponds and lakes is a vet emergency
Blue-green algae are really bacteria called cyanobacteria. In warm weather they can bloom on lakes, ponds, canals and slow rivers, and some blooms make toxins that attack the liver or the nervous system. A dog can be poisoned by drinking the water, swimming in it or licking the scum off its coat afterwards.
Symptoms can start within minutes to a few hours. Watch for vomiting, diarrhoea, drooling, trembling, staggering, fits, breathing trouble and collapse. There is no antidote, so speed matters. Rinse your dog's coat with clean water (wear gloves) and go straight to the vet.
You usually can't tell a toxic bloom by looking at it. The British Veterinary Association's advice is to keep dogs on a lead near water that might have a bloom, keep them from swimming in or drinking it, and follow any warning signs at the water's edge. Blooms can look like scum, spilled paint or pea soup. None of this applies to the farmed algae below, which are grown in controlled tanks and ponds.
Microalgae and seaweed are not the same thing
Microalgae are single cells, too small to see one at a time. Seaweeds are macroalgae, big plants you can pick up on a beach, like kelp and Ascophyllum nodosum. Both get called algae, and both end up as green or brown powders for dogs, but they do different jobs.
| Microalgae (spirulina, chlorella, Nannochloropsis) | Seaweed (kelp, Ascophyllum nodosum) | |
|---|---|---|
| What it is | Single cells, farmed in tanks or ponds | Large marine plants, harvested from the sea |
| Main contents | Protein (about 60 to 70% in spirulina), pigments, some omega fats | Fibre, minerals, iodine |
| Iodine | Low compared with seaweed | High, so it must be dosed carefully |
| What owners use it for | Coat, energy in older dogs, general nutrition | Teeth and breath, stool, minerals |
Yes, dogs can eat dried seaweed too, in small measured amounts, and because of the iodine it is dosed far more carefully than microalgae. The rest of this page sticks to microalgae.
Which alga does what
Four algae turn up in dog supplements. They are not interchangeable, and the dog research behind each is thin, so the last column matters.
| Alga | What it is | Why it's used | Dog evidence |
|---|---|---|---|
| Spirulina (Arthrospira platensis) | A farmed cyanobacterium with no hard cell wall | Protein, the blue pigment phycocyanin, GLA, an omega-6 fat | Two trials, one funded by a pet food maker |
| Chlorella (Chlorella vulgaris) | A green freshwater alga with a tough cell wall | Protein, chlorophyll, carotenoids such as lutein | One short trial in Beagles |
| Nannochloropsis | A tiny marine alga | EPA, the omega-3 fat that fish oil is valued for | The same Beagle trial |
| Schizochytrium (algae oil) | A marine microbe grown for its oil | DHA, the other fish-oil omega-3 | Used in dog foods as a DHA source |
Spirulina for dogs
Spirulina is the one most people have heard of. It's mostly protein, with all the amino acids dogs need, it's easy to digest because there's no tough wall around each cell, and its blue-green colour comes from phycocyanin.
The biggest dog trial is Satyaraj and colleagues (2021, Frontiers in Nutrition). Thirty Husky-cross sled dogs ate food with 0.2% spirulina or the same food without it for 42 weeks. The spirulina dogs made more antibody after a rabies vaccine, had more IgA in their stools, and their gut bacteria stayed more stable after a 10-mile run. IgA is the antibody that lines the gut. Nestlé Purina paid for the study and employed all the authors.
The second trial tested whether dogs will eat it at all. Stefanutti and colleagues (2023, Animals) gave spirulina tablets to 60 pet dogs for six weeks, doubling and then tripling the amount. Most took the tablets from an empty bowl or mixed into food. One owner in six said their dog didn't like them. The share of owners calling their dog's coat "optimal and shiny" went from 27% to 50%, though the change wasn't large enough to rule out chance.
Coat comes up in five reviews across our two algae products. In March 2023 Jenna H. wrote that after a month "the older 2 have more energy and softer coats while the younger dog has had a more settled stomach." Sanne R., who feeds raw, said her dogs "love the taste of the powder so much they usually eat the part of the meal where the powder is first." Our spirulina powder for dogs is organic Spirulina platensis, grown in raceway tanks in Europe.
Chlorella and Nannochloropsis
Chlorella's cell wall is hard enough that a dog can't break it down, so the useful products are "broken cell" or "cracked cell" powders. Whether you use a powder or chlorella tablets for dogs, check the label says broken cell.
Nannochloropsis is grown for its EPA. Our Microalgae Blend for Mature Dogs is the two together, organic European Chlorella vulgaris and Nannochloropsis.
The only dog trial on these two is Cabrita and colleagues (2023, Frontiers in Veterinary Science), in Beagles. Up to 1.5% of either alga in the food didn't upset digestion, chlorella nudged protein digestion up (from 70.6% to 73.9%), and both raised gut bacteria such as Turicibacter. No dog was ill. Given a choice, the Beagles preferred the bowl without the algae, so start with a pinch.
The blend has 10 reviews on our site, all five stars. Jennie wrote in June 2026 that it "works great for my 11 year old lab! She seems to have more energy and be more comfortable." Danielle C. (March 2023) noticed "their coats are much softer and smoother," and Sanne R. said "their fur has improved. Shinier and softer!"
Algae oil or fish oil
Fish don't make omega-3 themselves. They get EPA and DHA by eating algae, or by eating smaller fish that ate algae. Algae oil cuts out the fish, which suits a dog with a fish allergy and an owner who would rather not use fish oil.
Most algae oils are made from Schizochytrium and are mainly DHA. Nannochloropsis is mainly EPA. A whole-algae powder like our blend gives some omega-3 along with protein and pigments, but much less omega-3 per scoop than an oil does. If your vet has asked for a set omega-3 dose for arthritis or skin disease, use an oil with the EPA and DHA printed on the label, and follow the vet's number.
Is algae oil safe for dogs? At the label dose, yes, as long as it's a pet product or your vet is happy with a human one. Too much omega-3 of any kind can cause loose stools, so add it slowly.
How much to give
These are the amounts printed on our two packs. Start with a pinch and build up over a week or two. If you feed both spirulina and the blend, give half of each.
| Dog size | Spirulina (70 g jar) | Microalgae Blend (115 g jar) |
|---|---|---|
| Small | 0.65 g, about ¼ teaspoon (a jar lasts about 108 days) | 3 g, ½ to 1 teaspoon (about 38 days) |
| Medium | 1.3 g, about ½ teaspoon (about 54 days) | 6 g, 1½ to 2 teaspoons (about 19 days) |
| Large | 2.6 g, about 1 teaspoon (about 27 days) | 10 g, 2 to 3 teaspoons (about 11 days) |
Both powders stick best to wet food or kibble softened with a little water. Two reviewers mix the blend into yoghurt, one of them for a lick mat. Once a jar is open, use it within six months.
Side effects and who should ask a vet first
The usual side effect is a loose stool or a bit of wind at the start, and green-tinged poo from the pigment. In the 60-dog spirulina trial, 52 dogs finished six weeks with no problems. Three stopped because of vomiting and two because of diarrhoea, three of them after the amount was doubled or tripled. That's why we say to build up slowly.
Ask your vet before starting any alga if your dog
- is pregnant or feeding puppies, because there are no safety studies in breeding dogs
- is a puppy (check the minimum age with your vet)
- has an autoimmune disease or takes drugs that dampen the immune system
- takes a blood thinner, or any regular medicine
- has thyroid disease (microalgae are low in iodine, but seaweed blends are not)
- has a known allergy to iodine or moulds
Stop and call the vet if vomiting or diarrhoea lasts more than a day or two, or your dog seems unwell in any other way. A supplement is never the answer to a sick dog.
Choosing a safe product
The real risk with algae supplements is contamination, not the algae. Spirulina makes no toxins of its own, but it grows in the same conditions as cyanobacteria that do. Stefanutti and colleagues describe a dog that developed liver disease after three and a half weeks on a "blue-green algae" supplement made from Aphanizomenon flos-aquae, a lake-harvested alga. Testing found the supplement was contaminated with microcystin, the liver toxin from pond blooms.
So pick farmed algae from a named country, ask the seller whether each batch is tested for microcystins and heavy metals, avoid wild-harvested lake algae, and for chlorella check that it's broken cell. Our spirulina and blend are organic and grown in Europe.
Questions owners ask
Is algae safe for dogs?
Farmed supplement algae such as spirulina, chlorella and algae oil are safe for most dogs at the pack dose. Blue-green algae in lakes and ponds is not, and a dog that has been in it and seems unwell needs a vet straight away.
Can I give my dog spirulina every day?
Yes. It's meant as a daily food supplement. Use the pack amount for your dog's size and build up over a week or two.
My dog drank water with algae in it. What should I do?
Rinse the coat, keep your dog from licking it, and phone your vet now, even if your dog seems fine. Signs can start within minutes and there is no antidote.
What's the spirulina dosage for dogs per day?
On our pack it's 0.65 g (about ¼ teaspoon) for a small dog, 1.3 g for a medium dog and 2.6 g (about 1 teaspoon) for a large dog. Other brands differ, so go by the label of the one you buy.
Can dogs have spirulina and chlorella together?
Yes. If you give both, halve the daily amount of each.
How long before I see a difference?
The spirulina coat result above was measured at six weeks, and Jenna H. wrote her review after a month. Give it at least that long before deciding.
References
- Satyaraj E, Reynolds A, Engler R, Labuda J, Sun P, 2021. Supplementation of diets with spirulina influences immune and gut function in dogs. Frontiers in Nutrition 8, 667072.
- Stefanutti D et al., 2023. Oral palatability and owners' perception of the effect of increasing amounts of spirulina (Arthrospira platensis) in the diet of a cohort of healthy dogs and cats. Animals 13(8), 1275.
- Cabrita ARJ, Guilherme-Fernandes J, Spínola M, Maia MRG, Yergaliyev T, Camarinha-Silva A, Fonseca AJM, 2023. Effects of microalgae as dietary supplement on palatability, digestibility, fecal metabolites, and microbiota in healthy dogs. Frontiers in Veterinary Science 10, 1245790.
- British Veterinary Association, 2023. Stay away from blue-green algae and keep your dogs safe.
- Cornell University College of Veterinary Medicine, 2026. Blue-green algae poisoning (harmful algal blooms).
