If your dog flaps her head like a wet umbrella every time she leaves the water, her ears are telling you something. Damp ear canals are a comfortable home for yeast and bacteria, especially in dogs with long, floppy ears that block airflow around the canal. You do not need a full infection for it to be irritating.
Whole Dog Journal’s CJ Puotinen went shopping for dog ear plugs and found that real plugs barely exist for dogs. The companies making them had shut down or stopped making them. What you can buy are covers, and the list runs longer than you would guess: snoods, swim hoods, bathing caps, ear wraps, headbands, stretch tubes, and ear guards. She explains the options here.
For swimming, the options that work are snug and waterproof. A stretchy snood holds the ear flap against the head, so splashes and direct spray cannot reach the canal. Fabric hoods look similar and cut down on splashing, but they are not reliably water resistant.
What this means for your dog: if she swims often, shakes her head afterward, or has a history of ear infections, an inexpensive headband is worth trying before you start pricing vet visits. Those covers turn up in other places too. Vets use them to keep fluids out of the ears during dental work, long-eared dogs wear them at mealtimes, and they protect stitches and ear hematomas. Groomers put them on noise-sensitive dogs, where the compression also tends to settle them down.
Your dog will be back in the water long before you are ready for it (that is roughly what happened at a California dog surfing contest that ended early this month). A snood in the gear bag costs less than the first ear infection.