Tom Bonde Report on Green Lake

The following information is from Tom Bonde, Green Lake Property Owner member, who is working on a report on Green Lake. It is interesting to note that the presence of lake flies signifies that the lake has good quality and is not having a pollution problem.


Little information has been found relating to aquatic insects in the M. F. Crow River Watershed. The emergence of large numbers of the Burrowing mayfly, (Ephemeroptera), Hexigenia limbata, locally known as lake flies, has been a remarkable part of the Green Lake environment for as long as anyone can remember. Early newspaper accounts speak of their great abundance during their annual mating ritual that takes place in June. The species, which spends the greater part of their life cycle buried in the mud on the bottom of the lake, may be declining in abundance if early accounts are accurate. Population numbers, however, appear to vary from year to year and the emergence some years can only be described as massive. The deeper waters of the lake become anaerobic and this at times may be a factor limiting the size of the population. The Burrowing mayfly is sensitive to low oxygen concentrations and has been mentioned in the literature as a biological indicator; its mere presence being taken as an indication that a lake or river is in good shape. Its value as food for fish is high for they are readily taken by panfish as well as many other species.

Another common, if not abundant, insect are the midges (Diptera) which emerge on numerous occasions throughout the summer. These resemble the ever-abundant mosquito but differ in that they are non-biting. They rank high as food for fish. The larvae live in the bottom muds and have the ability to survive under polluted conditions. They have been considered to be an indicator species.

Without studies it is difficult to make any assessment of how mayfly and midge and other insect populations relate to the lake’s water quality. They are obviously a part of the food chain and play a part in the recycling of nutrients. How significant they are in say the phosphorus budget is open to question. They probably represent a net loss when considering the overall nutrient balance of a lake due to the fact that part of the population is either picked off by predators such as birds and spiders, or otherwise, carried away from the lake.

No attention has been given to the part played by other common aquatic insects such as Dragon and Damsel flies (Odonada), Caddis flies (Trichoptera) or semi-aquatics, such as Water boatmen (Corixidae), Water striders (Veliidae, Gerridae), and Backswimmers (Notonectidae).

The following is quoted from the Willmar Argus dated July 16, 1885:

" Parties going to Green lake Sunday say that for about a mile and a half along the lake shore the lake flies were numbered by the millions. They covered the horses, carriage, clothes, hair, and every available spot they could find. The faster the team went the thicker they seemed to be, and brooms had to be employed to remove them. They are said to be short lived, falling into the lake thick enough to blacken the water after an existence of a day or two."

The occurrence in mid-July seems unusual. The usual emergence nowadays is around the first two weeks of June. This prompts questions such as --- Was this the same critter (species) we see today? Has the lake warmed up causing an earlier emergence than in years past? We may never know the answers to these questions but to my way of thinking it is comforting to know that mayflies still exist even if they are something of a bother.

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