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To the Editor:

The Minnehaha Creek Watershed District’s lake grading method was developed in 1989. The grade shows how a 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. There are, of course, other factors that contribute to lake condition -- for example, aquatic plants, fisheries, harmful chemicals, over-use, and so on.

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 A (90% or higher). Crystal clear, beautiful. These lakes are exceptional and enjoyed recreationally without question or hesitation.

Grade B (70-90%). These lakes generally have good water quality but algae may limit swimming, particularly toward the end of summer.

Grade C (30-70%). Average quality. Swimming, boating, and fishing may be undesirable relatively early in the season. Algae blooms occasionally.

Grade D (10-30%). These lakes have severe algae problems. People are generally not interested in recreation on these lakes.

Grade F (Below 10%). Not enjoyable. Such a lake would have severe limitations to recreational use.

Three factors determined the grade.

1) Total Phosphorous (TP). Increase in phosphorous relates closely to increased algae, frequency of algae blooms, and the increased quantity of blue-green algae.

2) Chlorophyll-A (CLA). The green pigment in plants is essential to photosynthesis. A measure of its presence in water estimates algae abundance.

3) Secchi Disk (SD) transparency. The lower the Secchi Disk is visible, the clearer the water appears.

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.

The District’s waters are monitored on a regular basis. Data is collected by the Minnehaha Creek Watershed District, Three Rivers Park District, the Minneapolis Park & Recreation Board, and the Metropolitan Council. That data is used to note and correct problems wherever possible. Data is summarized and studies are conducted to identify potential improvements.

A yard and home might be a bad influence on the lake in your neighborhood. 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.

from Julie Westerlund

Education and Communications Manager

Minnehaha Creek Watershed District