Officials expect fish kills in most lakes throughout state

Published 12:26 am Thursday, April 3, 2003

By Staff
State Fisheries officials recently reminded residents to expect fish kills in many lakes throughout the state, noting that spring fish kills are most often natural and not related to environmental contamination.
Large-scale fish die-offs usually are one of three seasonal types, sparked by natural causes that cannot be controlled. The spring kill predicted by state fisheries biologists is related to the recent weather shift from a long, cold winter to above-normal, spring-like temperatures.
Winter fish kills occur in shallow lakes with excessive vegetation. Dying weeds rob dissolved oxygen from the water, and ice cover prevents lakes from drawing fresh oxygen into the water.
Fish also suffocate in particularly hot summer months, when plants consume large amounts of oxygen at night as part of the photosynthesis process and create large, oxygen-depleted areas in lakes. These summer kills claim fish in the hours just before dawn, when dissolved oxygen levels in shallow, weedy areas are at their lowest.
While it does occur, rarely are fish kills attributed to pollution or improper use of herbicides or other chemicals. Fish kills are unsightly, but most are not cause for alarm. However, if a chemical odor is noted in the area of a large die-off, or a strange water color or surface film is observed, residents should contact DNR Fisheries Division immediately at (517) 373-1280. More information on fish kills is available on the DNR web site at