Warm moisture trapped in the ears can cause infection, so its best to keep ears well ventilated and dry.
Especially with dogs that swim.

A list of some dogs prone to ear infections are:

Labs
Golden Retrievers
Boxers
Huskies
Bulldogs
Frenchies
Bassets
Dachsunds
King Charles
Boston Terriers
Shih-tzus
Rottweilers
Setters
Beagle

Any floppy eared mix, hound or swimming breed.

Swimmers like the beloved lab love to get in the water, so routine cleanings might be helpful.
Cleanings will also keep your attention on the ears, making you aware of any changes that need attending to.

Consider using dog friendly drying solutions, or just patting the ears dry after a swim.

Prevent problems with routine cleanings, and checking for any odors or redness.

Cleaning the ears.

Over the counter ear cleaners v. making your own. Both work

There are many affordable cleaners to choose from.
A mixture of one part hydrogen peroxide with one part water will also work.

Use soft cotton balls or cloth to wipe outer ears never go deep in the canal.
Always dry the ears after a cleaning, as water left in the ears can cause damage.

NEVER use cotton swabs in ears.

Understand that cleaners do not cure infections.
Yeast, bacteria, fungis all need specific medications to treat, never try clearing up infections on your own.

Knowing when to see your veterinarian.

Smell your dogs ears.
There should never be a strong odor, healthy ears are odorless.
Shaking or scratching at ears.
Any visible discharge or reoccuring build up of debris or wax, is not normal.

Note that ears should look pink and odorless, never red or irritated.

To keep cleaning ears that need attention could lead to further infection or problems.

Always seek veterinary assistance should any of these problems occur.

Reoccurring or persistant irritations may be a red flag.

Irritated ears can also be a sign of other problems, ie: food allergies, mites, foxtails, or infection.
So if the problem persists a veterinarian should always get involved.

Catching things quickly is the key to good health, and keeping veterinary expense down to just routine visits.