Water sustains life on earth. Aquatic plants and animals, terrestrial organisms — all require water for survival. This includes humans. Water is used for drinking, washing, watering and irrigation, and many commercial and industrial processes. The same water transports the effluent of wastewater treatment.
Water quality is generally determined by the following array of physical, chemical and biological properties:
A watershed's landscape and climate greatly influences interpretations of the properties measured to determine the health of streams, rivers, lakes and ponds. Each stream, river, lake and pond tends to exhibit and maintain a characteristic range of water quality measurements. This range may depend on factors such as the hydrology and geomorphology of the contributing watershed. The availability of fine sediments and the supply of groundwater are examples of landscape and climatic interactions that affect water quality.
Water quality changes when human activities upset the basic conditions of the stream system. These changes are often harmful from the standpoint of stream life and system balance.
"Understanding what constitutes 'good' water quality in Minnesota is difficult because of the wide variety of geographic and environmental conditions that exist in the state. Lakes and streams in the northern part of the state have different physical and chemical properties than those in the southern, eastern and western parts of the state. So, a water body in western Minnesota that is considered to be in good condition might be considered to be in poor condition if it were located in northern Minnesota."
(MN PCA Water Quality guide )
Explore the Water Quality Health Scores to see a series of index values that show health trends for water quality in Minnesota.