Water rises and falls against the shores, the moon pushed and pulling the waves. Your ki flows in much the same way, allowing you to tap into the power of the sea.

Water Whip

Your connection to the water has allowed you to tap into it to form lashing whips. Starting at 3rd level, the reach of your melee weapon attacks are increased by 5 feet. In addition whenever you hit with an unarmed strike or melee monk weapon you can spend 1 ki point to deal additional cold damage equal to one roll of your martial arts die plus your wisdom modifier. Whenever you use your flurry of blows, you can deal this additional damage without spending a ki point. You can deal this additional damage only once per turn.

Finally, any creature that takes this additional damage must make a strength saving throw (DC 8+your proficiency bonus+your wisdom modifier) or else be pushed or pulled (our choice) up to 10 feet horizontally in any direction.

Breathing Technique

Your time spent focusing on water has allowed you access to a strange supernatural method of ki fueled breathing. Starting at 3rd level, you can add your wisdom modifier to the number of minutes you can hold your breath before you suffocate, and you can do the same to the number of rounds you can survive without any held breath. Finally, you can't be forced to stop holding your breath against your will.

Traverse the Waves

Your knowledge of the ocean's movement allows you to move within it unimpeded. Starting at 6th level, you gain a swim speed equal to your walking speed and being underwater doesn't impose disadvantage on your attack rolls using unarmed strikes or monk weapons. In addition, you can use step of the wind or patient defense without spending a ki point, and can do so a number of times equal to your proficiency bonus. You regain all expended uses whenever you finish a long rest.

Channel Ocean

Your time spent studying the sea has allowed you to take on aspects of the creatures that live beneath its surface as well as the waves that rage upon it. Starting at 11th level, you gain blindsight out to a range of 10 feet as well as resistance to cold damage.  Finally, whenever you spend a ki point to deal additional cold damage using water whip, you can add two rolls of your martial arts die instead of one.

Aquatic Transformation

At the apex of your power, you become a natural extension of the moon and the waves. Starting at 17th level, your melee reach increases by a further 5 feet and you can use your water whip with both of your flurry of blows attacks provided you haven't already used it on your main action. In addition, you become immune to cold damage instead of resistant and your blindsight range increases to 30 feet, and you gain the ability to breathe underwater without suffocating. Finally, while submerged fully in water you can use your flurry of blows without spending any ki points.