From Wikipedia:
 Quote:
Eutrophication is an increase in chemical nutrients � compounds containing nitrogen or phosphorus � in an ecosystem, and may occur on land or in water. However, the term is often used to mean the resultant increase in the ecosystem's primary productivity (excessive plant growth and decay), and further effects including lack of oxygen and severe reductions in water quality, fish, and other animal populations.

Taken to the extreme, eutrophication means scummy water chokingly filled with algae. When the algae dies, its decay uses up all the available oxygen in the water cause a large loss of fish and other aquatic life. So you can see why one would want to avoid that level of nutrient buildup.

"Live like you'll die tomorrow, but manage your grass like you'll live forever."
-S. M. Stirling
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