Water Quality

Water Clarity

The transparency of lake water, typically measured by Secchi depth, a primary indicator of water quality and recreational suitability.

What It Means for Your Lake

Water clarity refers to how far you can see into a lake and is the water quality characteristic most immediately noticeable to lake visitors. Clarity is determined by the amount of suspended particles in the water, including algae cells, sediment, dissolved organic matter (tannins from decaying vegetation), and inorganic particles stirred up from the bottom. In Minnesota and Wisconsin, water clarity varies enormously: crystal-clear lakes in the Boundary Waters and Northern Highland regions may have visibility exceeding 25 feet, while turbid prairie lakes in southwestern Minnesota may have less than 6 inches of visibility. Water clarity is primarily measured using a Secchi disk, making it the most accessible water quality metric for citizen scientists and lake association volunteers. The Minnesota Pollution Control Agency Citizen Lake Monitoring Program, one of the largest in the nation, trains hundreds of volunteers to take weekly Secchi readings throughout the summer season. Clarity affects recreation directly, swimmers prefer clear water where they can see the bottom, and water-skiers and divers need adequate visibility for safety. Clarity also influences property values: studies have shown that every one-meter increase in Secchi depth is associated with a 2% to 6% increase in lakefront property values in the Upper Midwest. LakeQuality weights water clarity at 35% of the overall grade, the highest weight of any single metric, because it is the best single indicator of overall lake condition and the most relevant metric for recreational users.

Frequently Asked Questions