out of one's depth
In water so deep that one cannot stand and may be at risk of drowning.
noun
the vertical distance below a surface; the degree to which something is deep
Measure the depth of the water in this part of the bay.
the distance between the front and the back, as the depth of a drawer or closet
the intensity, complexity, strength, seriousness or importance of an emotion, situation, etc.
The depth of her misery was apparent to everyone.
The depth of the crisis had been exaggerated.
lowness
the depth of a sound
the total palette of available colors