The Underwater World is an additional three-level event that becomes available when the player reaches level 6.

You can enter the event by tapping the bathysphere in the farm's main window.

Oxygen is a special resource required for participating in the Underwater World. You can use it to clear the underwater location of objects, complete tasks and advance the search for quest items.

Oxygen isn't infinite — it builds up. A full oxygen bar has 50 units of oxygen. Oxygen regenerates at a rate of 1 unit per 90 seconds.

After an event finishes, all unused resources are automatically exchanged for coins.

Unfortunately, this can happen if you didn't have enough time to complete the event. You can always try again next time.