Negative buoyancy means that an object is heavier than water and sinks.
A negative buoyancy situation can be dangerous and therefore should not be taken lightly.
Because negative buoyancy decreases the amount of force it takes to submerge someone, it can be easy for a negative buoyancy person to accidentally go below water and drown.
Negative buoyancy is most commonly found in children who have not yet learned how to swim because they find swimming easier when submerged head first into the deep end of the pool or ocean.
Once kids learn how to swim properly they no longer need negative buoyancy to help them stay afloat as their strength builds up.
So if you want to swim underwater, then you must master the art of maintaining negative buoyancy.