Secchi Transparency Slide Show
Minnesota is known for its many lakes; however, the quality and condition of these waters range from exceptionally good (oligotrophic) to extremely poor (hypereutrophic).
Secchi transparency (clarity) is a quick and easy measurement of lake's water quality. Secchi transparency provides an indirect measure of the amount of suspended material in the water; which in many Minnesota lakes - is the amount of algae in the water. Secchi transparency (clarity) can vary greatly among Minnesota’s lakes and tends to decrease as algal concentrations increase over the summer. Watch the slide show that follows the change in Secchi transparency for Minnesota lakes from four different classifications of lake water quality.
You can also watch the water clarity of each of the four lake groups as they change over the summer, including some underwater shots.
Please note: If you don't see the photos in the slideshow below, you'll need to install or upgrade the Flash player on your computer to the minimum version 7.0 to view the slide show. If the photos are visible but appear distorted, try clicking on the refresh button on your browser or reload this page. Download Flash Player 
Compare All
Minnesota lakes vary in size, shape, depth and overall water quality. The following Secchi images were taken from four distinct lake qualities in May, June, July, August, September and October. Watch how the water clarity changes over time in response to increases or decreases in algae concentrations.
- MAY: In spring, lake water is cool, limiting algae growth. As a result, transparency is very high on most Minnesota lakes.
- JUNE: As temperatures rise, lake waters warm and algae and other aquatic plants being to grow. Transparency may begin to decline but should still be quite good on the oligotrophic and mesotrophic class lakes. There will be a marked reduction in clarity though on eutrophic and hypereutrophic lakes.
- JULY: Algae growth has likely become more pronounced; however, on oligotrophic lakes this may be barely noticeable as compared to mesotrophic, eutrophic and hypereutrophic lakes. Nuisance and severe nuisance algal blooms may now be present on eutrophic and hypereutrophic lakes.
- AUGUST: Algae growth often peaks in August. Nuisance and severe nuisance blooms are common on most eutrophic and hypereutrophic lakes. Water clarity is often at a seasonal minimum for most lakes.
- SEPTEMBER: Transparency may remain low, particularly on eutrophic and hypereutrophic lakes. Significant algae blooms can still occur if temperatures remain warm.
- OCTOBER: Water temperatures have cooled significantly and most algae and aquatic plants have died back. Transparency should be much improved over mid-summer months. Fall algae blooms may occur in the lake following fall turnover.
See slideshows of the four lake groups:
