Swimming in the sea in Mallorca during April is possible, but it is certainly "bracing" rather than tropical. The Mediterranean water temperature in April typically hovers around 15°C to 17°C (59°F to 63°F). For most casual swimmers, this is considered quite cold, especially since the air temperature is usually in the high teens or low 20s. You will see some locals and brave tourists in the water, but most people prefer to sunbathe on the sand or use their hotel's heated pool. However, April is a fantastic month for water sports like kayaking or paddleboarding, as the sea is often calm and the beaches are not yet crowded with the summer rush. If you are a fan of "wild swimming" or cold-water therapy, you will find the crystal-clear coves (calas) like Cala Mondragó or Es Trenc absolutely beautiful, but for a long, comfortable swim, you might want to wait until June when the water reaches a much more pleasant 22°C.