Turbidity describes the clarity in the water, looking at the dissolved solids, including clay, silt, plankton, industrial wastes, and sewage.
With higher levels of turbidity the watercan not support a diversity of aquatic organisms. Water becomes warmer and dissolved oxygen levels fall as less light penetrates the water. Photosynthesis is slowed down, which further drops the oxygen level.
All this can make it impossible for an organism to survive. Excessive sediments can also clog gills of fish which can become a major problem.