You create a small sphere of breathable air around your head, allowing you to dive underwater without the need for air. The sphere provides a comfortable environment for breathing, effectively protecting you from the surrounding water.
As you gain levels, the strength and resilience of the sphere increase, allowing you to dive deeper without risk of collapse due to water pressure. The sphere can withstand pressure equivalent to a depth of 10 feet + 10 feet for each character level you have attained.
If you exceed this depth while the sphere is active, the bubble collapses and you immediately must make a Constitution saving throw (DC = 8 + your proficiency bonus + your Constitution modifier) or begin to suffocate.
* - (a droplet of water)