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A diver in the halocline becomes difficult to see.

  Salt water is more dense than fresh water, and so light rays are diffracted when they pass through the halocline.  This can give rise to a range of unusual visual effects.  As the photos on this page illustrate, a diver's swimming motions will stir up the salt and fresh water like salad oil and vinegar.

Because there is active rock dissolution in the halocline, there is also fine silt on the floor, walls, and ceiling of the cave.  Divers are trained to use special finning techniques to minimize the stirring of silt.  Nonetheless, a diver's bubbles can dislodge the silt from the ceiling, reducing visibility for the divers following him, and for his return journey.  The effect is known as percolation and is one reason why specialist training is required to dive in caves. 

A cave warning sign found in fresh water...   ...and another viewed through the halocline.