Yes, swimming in Croatia in late September is not only possible but is often considered the "sweet spot" for savvy travelers in 2026. While the air temperature begins to cool to a pleasant 21°C to 24°C, the Adriatic Sea retains the heat absorbed during the scorching summer months, with water temperatures hovering around 22°C to 23°C. This is significantly warmer than the water in June. The southern regions, such as Dubrovnik, Hvar, and Korčula, stay warm the longest. The primary advantage of swimming in September is the dramatic decrease in crowds; you can often find a private cove or a spot at the famous Zlatni Rat beach without fighting for space. However, late September can bring the "Bura" or "Jugo" winds, which can make the water choppy and the air feel cooler when you exit the sea. It is wise to bring a light jacket for the evenings, but during the day, the sun is still strong enough for a classic beach holiday without the intense 35°C+ heat of August.