Thank you to a reader who referred us to an article in the Green Bay Press Gazette headlined “Dangerous blue-green algae creeps in behind heat.” (see the link under comments to the Connecting the Dots post)
Certainly the heat has a lot to do with algae growth. It’s not the only factor, however. What the article does not mention is that to grow, algae requires nutrients which come from both naturally-occuring decomposition of plant materials and runoff from land. The blue-green algae, called Cyanobacteria, talked about in the article is a problem on inland lakes and ponds, including Krohn’s Lake as pictured in the article. Because of the lack of rainfall and excessive heat, many inland lakes don’t have the usual water flow. Pockets of stagnant water are breeding grounds for the blue-green algae.
The other algae of concern in Kewaunee County, especially along the lakeshore, is called Cladophora. Cladophora is green algae, and while not as toxic as blue-green algae still presents a significant health risk as it accumulates and decomposes on the beaches and shoreline. The cycle of clearer water caused by the invasive zebra mussels allows sunlight to penetrate deeper in the water encouraging Cladophora to feed on nutrients washed into the lake and grow on the rocky bottom. Wave action tears the algae off the rocks and brings it ashore where it accumulates and rots in the hot sun. As it decomposes it release dangerous hydrogen sulfide gas and provides a perfect environment for growth of e-coli bacteria. That can often lead to beach closings because of the health risk to swimmers.
So be careful before you plunge into your favorite swimming spot this summer. And if you see a potential problem, either a new algae bloom or possible contamination risk from runoff, call the DNR. It appears they’re paying more attention to water quality in Kewaunee County.