Protecting the Waters:
The Issue of Phosphorous

Causes and sources
Problem extent
Efforts and progress
Looking to the future

Rain to Rivers Program

UWEX Natural Resources Education


The Problem Extent

Extent in the Red Cedar Basin

Many lakes in the Red Cedar Basin are susceptible to excess phosphorus loads, and thus, algal blooms, especially man-made lakes (impoundments). Entire lakes can be covered when an algal bloom is severe, and wind-blown bays where a lot of the surface algal mat can accumulate, will often display worse conditions. In the Red Cedar River, often times the water released from the flowage dams contains a significant amount of algae; enough to cause the river below these dams to look almost as green as the lakes themselves.

The algae and the other nutrient pollutants in the lake eventually find their way farther downstream in the Red Cedar River, emptying into the Chippewa River, then the Mississippi River, and eventually being released into the Gulf of Mexico. Because of all the pollutants being washed into the Gulf from farm fields and cities, along with effluent from water treatment plants, chemical plants and refineries, there is a zone of depleted oxygen, or a "dead zone" near the mouth of the Mississippi River. In this portion of the Gulf, which sometimes can be the size of the state of New Jersey, there is very little aquatic life because organisms that live in the water need dissolved oxygen, and if the oxygen is depleted they can't survive.

Harmful Effects from Algal Blooms
The toxins released by blue-green algae can be very harmful to people and pets. Many of these toxins are powerful neurotoxins, and if ingested in large enough quantities, can be fatal. We often hear of family dogs dying after swimming and ingesting lake water during a severe algal bloom. These toxins can also cause severe skin irritation after exposure, and people near the water during severe blooms have occasionally reported respiratory problems. Although the level of risk is not certain when eating fish or shellfish caught in a river or lake during a severe algal bloom, they should be consumed in moderation. Additionally, the guts and organs of the fish, where toxins can accumulate in higher quantities, should not be eaten, and care should be taken when cleaning the fish to prevent any fluid or tissue from the organs from contaminating the fillets. The Wisconsin Department of Natural Resources website has more information about the dangers posed by the presence of blue green algae.

There are many other impacts from severe algal blooms. Objectionable water clarity and smell prevents many people from recreating on the lakes, and also can lead to lower property values, all having a negative affect on local economies. Severe algal blooms also deplete oxygen in the lake which can lead to fish kills. Additionally, research from Northern Wisconsin has shown that excessive algal growth in lakes is linked to deformities in frog populations.

(Click here for a slide show on this topic)

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