Regional Context: Lakes

Most Midwestern lakes are said to be "phosphorus limited".

Phosphorus - a nutrient - directly determines algae growth because it is the nutrient in the lowest supply. Lakes can be very sensitive to additions of phosphorus.

Human activities add phosphorus to lakes in many ways. Storm sewers, ditches, tile lines, and overland runoff carry extra phosphorus off the land and into a lake. When the concentration of nutrients in a lake reaches too high a level, growth of algae increases and the lake's water clarity tends to decrease. This condition can result in a loss of submersed aquatic plants.

Human activities also accelerate erosion -- increasing the amount of soil that washes from the land into a lake. Soil limits transparency (the clarity of the water) while it is suspended. Once it settles and covers the lake bottom, soil degrades habitat for fish spawning and for bottom-dwelling creatures.

Excess phosphorus and sediment in a lake result in visible impacts to lake water quality. There are many other pollutants that affect water quality and lake ecology in a less obvious way. These include pollutants such as pesticides, bacteria, and salt that may enter lakes as a result of human activities like farming, lawn care, failing septic systems, and road maintenance.