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What is Secchi depth?

A Secchi disk is a round plate that’s painted black and white. The disk is attached to a rope. The rope is lowered into the lake until it’s at a depth where it can no longer be seen.

This is called the ‘Secchi depth’. It helps to measures the clarity of the water and the general ‘health’ of the lake.

Clear water lets light penetrate more deeply into the lake than murky water. Sunlight is needed for the growth of phytoplankton. Phytoplankton is the basic food source in a lake. It needs sunlight, phosphorus and nitrogen to grow.

Secchi Readings

  • High Secchi reading = clear water
  • Low Secchi reading = turbid or coloured water