The Minnehaha Creek Watershed District’s lake grading method was developed in 1989. The grade shows how your lake measures up compared with other area lakes. Grades are an indicator of the perceived condition of the open water. Three water quality measurements are combined to create each grade (see below). There are, of course, other factors that contribute to lake condition—for example, aquatic plants, fisheries, harmful chemicals, over-use, etc.
Understanding Your Grade
The grades consider what is average or normal for lakes in a given area. What is a “C” in one part of the country might not be a “C” elsewhere. But, within the seven-county metro area, grades can be compared.
Grade |
Relative Ranking |
Description |
A |
90% and up | Crystal clear, beautiful. These lakes are exceptional and are enjoyed recreationally without question or hesitation. |
B |
70 - 90% | These lakes generally have good water quality but algae may limit swimming, particularly toward the end of summer. |
C |
30 -70% | Average quality. Swimming, boating and fishing may be undesirable relatively early in the season. Algae blooms occasionally. |
D |
10 - 30% | These lakes have severe algae problems. People are generally not interested in recreation on these lakes. |
F |
Lowest 10% | Not enjoyable. Such a lake would have severe limitations to recreational use. |
Factors in Your Grade
- TP is the total phosphorus measure. Increase phosphorus relates closely to increased algae, frequency of algae blooms and the increased quantity of blue-green algae.
- CLA is chlorophyll-a or the green pigment in plants. Chlorophyll-a is essential to photosynthesis. A measure of its presence in water estimates algae abundance.
- SD is the Secchi disk transparency. The lower the Secchi disk is visible, the clearer the water appears.
Improving Low Grades
Getting a better grade takes extra work. It might mean changes in drainage patterns, filtration or detention of storm water. Not all lakes have the same potential (shallow lakes can have only so much Secchi visibility). It’s up to everyone to help water quality live up to its potential.
Monitoring
The District’s waters are monitored on a regular basis. Data is collected by the MCWD, Hennepin Parks, the Minneapolis Park & Recreation Board and Metropolitan Council. That data is used to note and correct problems wherever possible. Data is summarized and studies are conducted to identify potential improvements.
More Information
Your yard and home might be a bad influence on your neighborhood lake. Keep your grades up, prevent wastes from entering the water through the street storm drains. Storm drains are a direct, untreated route to the nearest lake or stream.