Minecraft wiki entry for Combat, associated text: Acting the same as zombies, Drowned instead spawn in oceans, rivers and underwater ruins‌[JE only]. Normal zombies can also drown in water and be converted into drowned after 30 seconds. They are easy to kill like normal zombies, except if a drowned mob spawns holding a trident, which can be dangerous if players are not protected with armor. It's recommended to wear armor with Projectile Protection.