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No one likes the sight — or the smell — of a sea of dead fish washing up to shore on area lakes.

But as the ice comes off of lakes this time of year, winter kills are relatively common in Minnesota. This spring the kills may be worse than normal because of the way last winter played out.

Winter kills are natural and can have some beneficial effects.

But there are also summer mass fish die-offs on Minnesota lakes. Those occur when the water warms and holds less oxygen and stresses fish making them more susceptible to diseases that can kill them.

Evidence is growing to suggest human activity is likely to create conditions that dramatically increase summer fish kills.

Winter kills happen because of a loss of oxygen in a lake. It’s a phenomenon that happens almost exclusively on shallow lakes, of which we have many in southern Minnesota.

Submerged vegetation and algae create oxygen through the process of photosynthesis. During the winter, oxygen production is reduced if heavy snow covers the ice, blocking sun from spurring photosynthesis.

Fish kills are particularly hard on game fish, but they can be beneficial to lakes with large numbers of carp, by thinning out their numbers.

Studies, including one by the University of Arkansas, show that human driven climate change will increase summer fish kills because steadily warming temperatures will bring warmer water that spurs algae growth, reduced oxygen levels and more infectious diseases in fish. The study, reported by MPR News, used decades of information on nearly 9,000 lakes in Minnesota and Wisconsin.

The study paints a bleak future for Minnesota lakes, especially the shallower lakes that are prevalent in southern Minnesota.

The study predicts that based on the current pace of climate change, there is expected to be a 600% increase in fish kills by 2100.

Beyond fish kills, warmer water will increase the deterioration of water quality in lakes, reducing recreational use.

It’s a frightening outlook for a state that has such a long and rich tradition with its lakes and fishing.

It is yet another reason for us to increase efforts to slow climate change to lessen the potential damage it will do.

— Mankato Free Press, April 18