Phosphorus Management Activity
Phosphorus and Transparency


Michigan Environmental Education Curriculum
Water Quality - Pollutant Sources and Impacts

Secchi DiskWater clarity or transparency is an important indicator of water quality in lakes. Clarity is measured using a Secchi disk, a white (or black and white) plate which is lowered into the water until it can no longer be seen: the deeper you can see it, the better the transparency. The Secchi disk depth can range from less than 1m in highly eutrophic lakes to more than 20m in Lake Superior.

The addition of excess phosphorus to lakes stimulates algal growth (eutrophication) and the water becomes green and turbid (low transparency, shallow Secchi disk depth). Transparency can be improved by reducing phosphorus inputs to the lake.


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