Swimmer’s Itch in Dogs: What Minnesota Pet Owners Need to Know

If you’ve ever dealt with itchy, bumpy skin after a lake swim, you already know how uncomfortable swimmer’s itch can be. But did you know your dog can get it, too? Swimmer’s itch—clinically known as cercarial dermatitis—is a skin rash caused by tiny parasites that live in freshwater lakes and ponds. While these parasites can’t survive in your dog’s body, they can still cause an allergic reaction that leaves your pup scratching and miserable.

What Causes Swimmer’s Itch?

Swimmer’s itch is caused by parasitic larvae called cercariae that are released into the water from infected snails. The natural hosts of these larvae are birds, but when they come into contact with the skin of humans or dogs, they burrow in and die. This process triggers an allergic reaction—such as an itchy, often painful rash.

While swimmer’s itch isn’t contagious, it is a sign that your pet was exposed to water containing these parasites.

Why It’s a Concern in Minnesota and Wisconsin

If you’re a Midwest pet parent, swimmer’s itch should always be on your radar. Minnesota and Wisconsin are home to thousands of lakes—many of which become warm and shallow during summer. This creates perfect conditions for the parasite cycle to thrive.

Popular spots like Lake Minnetonka, White Bear Lake, Mille Lacs, and the Chain O’Lakes often are bustling with plenty of people—and their dogs. These shallow, quiet swimming areas near shore are exactly where the parasites tend to congregate.

It’s good to know that not all lakes are monitored for swimmer’s itch. It is best to assume it could be present, especially during the peak summer months when it is hottest.

Signs Your Dog Might Have Swimmer’s Itch

Just like people, dogs develop swimmer’s itch in areas where skin is most exposed. Check for these signs after your dog has spent time in the lake:

Red, raised bumps—check their belly, inner thighs, and groin areas especially
Intense itching and scratching
Restlessness, whining, or visible discomfort
Licking or chewing at affected areas
Open sores or skin infections from over scratching

Symptoms usually show up within a few hours and can last a few days. In many cases, the rash will eventually take care of itself, but if your dog seems extra uncomfortable, a visit to the vet, is a good idea.

How Is Swimmer’s Itch Diagnosed?

Because swimmer’s itch isn’t caused by bacteria or a visible parasite, there isn’t a specific way to test for it. Veterinarians will typically base their diagnosis on:

Recent exposure to freshwater
Location and appearance of the rash
Ruling out other potential causes like hot spots, flea allergies, or bacterial infections

If your vet suspects a secondary infection, they may recommend a skin cytology or culture to provide the best course of treatment options.

Treatment Options for Dogs with Swimmer’s Itch

Most mild cases can be treated at home with a little TLC. Here’s what helps:

At-home relief for minor irritation:

Rinse your dog well with clean water right after lake time
Use a soothing oatmeal-based or medicated shampoo.
Apply a vet-recommended anti-itch spray or topical cream.
Use oral antihistamines like Zyrtec or Benadryl (but only under the guidance of your veterinarian!)

More serious cases:

Your vet may prescribe a corticosteroid cream or oral medication
Antibiotics could be needed if an infection has started
An e-collar can prevent further scratching and additional skin damage

⚠️ Note of caution: Many human products (like OTC hydrocortisone creams) are NOT safe for pets. The cream in your medicine cabinet could contain ingredients that are toxic or harmful to dogs like fragrances, dyes, and preservatives. Always talk to your vet before applying anything new to your pet’s skin.

Tips to Prevent Swimmer’s Itch in Dogs

You don’t have to avoid letting your dog in the lakes—but there are some things you can do to prevent it:

Rinse and dry after a swim
Wash fur and skin folds and sensitive areas with clean water.
Avoid warm, shallow, weedy areas
These tend to be the hotspots for swimmer’s itch. Let your dog swim in deeper, moving water whenever possible.
Limit shoreline digging or lounging, and avoid it entirely during the hottest months
Parasites often hang out in the muck near shore.
Check local lake advisories
Some counties in MN and WI post swimmer’s itch alerts—stay informed in your area, but also be cautious even if there isn’t a warning posted.
Use pet-safe barrier products
Some balms or protective creams can help reduce exposure, especially on the belly or groin.
Bring your own drinking water
Drinking from lakes can expose dogs to other potential dangers like blue-green algae.

When It’s Time to Call the Vet

Mild itchiness after swimming could resolve on its own, but sometimes it’s necessary to call for professional treatment, give your vet or veterinary dermatologist a visit if:

Your dog is constantly scratching or seems in pain
The rash gets worse after a day or two
You notice open sores, pus, or a bad odor developing
Your dog has a fever, low energy, or stops eating

Early treatment can prevent secondary infections and get your pet feeling comfortable faster.

How Our Team Can Help

If your dog struggles with swimmer’s itch—or any other ear or skin-related issue—be sure to get them seen by your primary vet. Haarstad Veterinary Dermatology is always here to help as well, if it is a recurring concern. With offices in both Osseo/Maple Grove and Duluth, MN and serving surrounding areas across western Wisconsin, eastern North Dakota and other parts of MN through on-site clinics, we specialize in diagnosing and treating skin conditions in dogs and cats.

Our experienced team is here for you to provide:

Skin evaluations and diagnostics unidentifiable rashes
Tailored treatment plans using the most up-to-date dermatologic care
Solutions for recurring issues or allergy-prone pets
Kind, knowledgeable support that puts your pet’s comfort first

We understand how important lake life is in the Midwest—and we’re here to help you enjoy it without the itch. Whether it’s a one-time rash or a recurring problem, we’ll work with you to find the right solution.

Swimmer's itch may sound like a minor nuisance, but it can cause a lot of distress for your dog. Knowing how to prevent it—and when to seek help—makes all the difference. When in doubt, rinse your pup after every lake swim, avoid risky shoreline spots, and watch closely for signs of irritation.

And if that rash won’t go away or your dog seems miserable, don’t hesitate to call Haarstad Veterinary Dermatology. We’re here to keep your pet’s skin healthy so every swim and family lake day can be safe and fun for everyone.

Learn more or request an appointment on our website at HaarstadVeterinaryDermatology.com.