Missing Aquatic or Flight Form

All Druid class travel forms in the most recent expansion of World of Warcraft have been merged to the same button on your user interface. When you are in an area where flying is allowed and you have unlocked it, using the button will automatically use flight form. When you're in water that is deep enough for swimming, travel form will turn into aquatic form.

In Classic WoW, you will need to unlock your various forms through questing. Quests are available at the appropriate level from your Druid class trainer.