What is the most likely diagnosis for a patient presenting with ear pain, drainage, and erythematous canal after swimming?

The symptoms described—ear pain, drainage, and an erythematous canal—are indicative of external otitis, commonly known as swimmer's ear. This condition typically occurs when water remains trapped in the ear canal, creating an environment conducive to infection from bacteria or fungi. The erythematous appearance of the ear canal suggests inflammation and irritation, often accompanying the pain and discharge seen in an active infection.

In contrast, chronic otitis media is usually associated with a history of middle ear infections and often presents with more systemic symptoms rather than localized canal symptoms. Myringitis, which involves inflammation of the tympanic membrane, can cause ear pain but typically does not present with drainage from the canal. Otosclerosis is a condition affecting the bones of the middle ear and leads to hearing loss rather than the symptoms described in the scenario. Therefore, the presentation aligns most closely with external otitis, making it the most likely diagnosis.