(7-8-20) From the Lake Improvement Association –
An update on current Grand Lake St. Marys water conditions, courtesy Dr. Stephen Jacquemin, Associate Professor of Biology at Wright State University-Lake Campus:
Oxygen concentration has dropped precipitously in the lake over the past week as levels have fallen to between 0 and 1 mg/L during the night across the majority of the basin. This is far below what is required to sustain fish life in the lake. As a result, a large scale fish die off began several days ago and continues to progress. This die off has occurred across the lake but does seem to have affected some areas more than others.
Initial surveys across the middle of the lake indicate that a variety of species have been affected – including Freshwater Drum, Channel Catfish, Gizzard Shad, Largemouth Bass, Crappie, Bluegill, Green Sunfish, Walleye, Hybrid Walleye/Sauger ‘Saugeye’, Common Carp, Quillback, Yellow Perch, White Sucker, Spotfin Shiner, Fathead Minnow, Bluntnose Minnow, Goldfish, and Yellow Bullhead.
Unfortunately, this die off will continue until oxygen concentrations begin to increase. Note that low levels of oxygen at this time are a combined result of summer heat as warm water holds less oxygen then cool water, lack of wind or wave action as agitation of water helps fold oxygen into the water column from the air, microbial breakdown of organic material along the lake bottom as these microbes utilize oxygen in the water during metabolism, as well as algal bloom activity as cyanobacteria take up oxygen in the evening when not photosynthetically active compared with their production of oxygen during the day when photosynthesis.
From the ODNR –
Boaters, anglers and other visitors may notice that Grand Lake St Marys is experiencing a significant fish die off caused by a combination of hot temperatures, no precipitation, and minimal wave action. Events like these are not uncommon and do not indicate any change in lake health. Low oxygen levels in the lake will persist until weather conditions change. ODNR will continue to monitor the lake and make updates, as needed.