DES MOINES, Iowa (AP) — Iowa officials say the harsh winter is expected to affect some fish populations in the state. The state Department of Natural Resources says lakes and ponds experience natural winter fish mortality. But Jim Wahl, supervisor for fisheries in northwest Iowa, says officials are expecting to see more lakes and ponds affected this time around. Wahl added a few lakes are experiencing oxygen levels that are lower than normal.

Officials say lakes under snow are shut off from sunlight that helps aquatic plants. That has a ripple effect on photosynthesis and the flow of oxygen into the water. DNR officials have placed aeration systems at a few lakes with a history of winter kills. Those systems keep a section of a lake from freezing.