Simply Science: Swede Lake Fish Kill

WATERTOWN, Minn. - The shores of quaint Swede Lake in Carver County are littered with dead crappies, who are the victims of a long, hot summer that recorded 90 degrees as recently as Sept. 11.

"Increased temperatures, lower oxygen and algae blooms, essentially cause a triple whammy for these fish," said Taylor Polomis, who is with theDNR Fisheries West Metro Office.

Fish are cold blooded, so as the water warms up, they need more oxygen to support their breathing. Unfortunately for them, warmer water makes that difficult.

"The higher the temperature, the less dissolved oxygen in the water, so these fish have less oxygen to breathe," Polomis added.

Coinciding with the lower oxygen levels is an increase in bacteria and viruses that also compete for the oxygen.

Fertilizer runoff from surrounding farm land helps create the third factor.

"What makes the crops and your grass grow well is also very fertile in the water and causes algae blooms," says Polomis.

Those blooms also deplete the oxygen.

The large fish kills aren't all bad. They do help prevent overcrowding in a small shallow lake like Swede Lake,a bit like pushing a reset button.


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