This season Lake Manitou has not yet had a full algae bloom with the exception of the Waugh channel area*, whereas in previous years we’ve had several blooms by now. This may change in August and September, in part due to increased air and water temperatures. A major factor that influences algae blooms are external nutrient loads arriving into the lake primarily from the Hardy Jennings drain. Other factors are water temperature de-stratification and anoxia.
In most healthy natural lakes the water is divided into three distinct temperature stratification layers. The surface is warmest, the center is cooler and the bottom layer is coldest. When the lake water is consistently mixed, (especially in Lake Manitou at only 73 acres and an average depth of 11 feet), we lose these necessary temperature layers of a balanced ecosystem and the lake becomes de-stratified. Dr. Jude points out in his 2011 Lake Manitou fish study, [Page 48], “Based on our water temperature and water quality measurements in the main basin of the lake, it appears that boat traffic in this basin de-stratifies the lake. This mixes nutrients on the bottom into surface waters where they can be used by aquatic plants and algae.” What he is saying is that the lake is too small for high speed activities. An analogy is using a kitchen mixer in a bowl at high speed. It’s another anthropogenic (man made) influence within the lake that facilitates algae blooms.
Anoxia occurs when there is no oxygen in the water at the lake floor. This creates a chemical reaction which releases nutrients from the lake floor into the water column that would otherwise remain there. The nutrients facilitate algae blooms.
Water quality could be greatly improved if we were to substantially reduce nutrient loads and soil sediment from entering into the lake. Further improvement could be made if we limited watercraft horsepower to 50 horse power.
To reduce anoxia, it would take an engineered air diffuser system in several parts of the lake. Several years ago we had an environmental company representative survey our lake for such a system. His analysis was that until we are successful in substantially reducing the negative influences from the drain, a diffuser system will be limited in making an improvement in overall water quality.
It is also critical that all residents with shore lines eliminate lawn fertilization anywhere near the water. Pet waste should be picked up regularly and the lake water would benefit greatly with buffers strips 20 to 50 feet wide at the shoreline. The buffer strip is a no mowing zone containing native shoreline plants and shrubs. The buffer strip helps catch fertilizer runoff and stabilizes shoreline erosion.
This is a link to a short article about algae posted July 28, 2020 from EGLE. https://www.michigan.gov/mienvironment/0,9349,7-385-93394-534773–,00.html
This is a link to Michigan Natural Shorelines. https://www.mishorelinepartnership.org/
*Due to agricultural runoff the Hardy Jennings drain continues to add nutrients and nutrient laden soils into the lake at Waugh road. This dramatically increases algae production in the channel as well as influencing algae production in the main body of the lake.