Minecraft wiki entry for Things_not_to_do, associated text: Should the player need to dig underwater for long periods of time, a helmet enchanted with Aqua Affinity and/or Respiration, a turtle shell, or a Water Breathing potion can be used. A conduit can also be built if the player expects to be underwater even longer. The player should be careful near ocean monuments, as the elder guardians inflict Mining Fatigue III, drastically reducing mining speed.