CHICOPEE, Mass. (WWLP) – The Massachusetts Department of Fisheries and Wildlife is asking residents to report any winter fish kills they find at local ponds.

Due to thick ice and heavy snow during the winter months, ponds can have lower dissolved oxygen levels. Without sunlight penetrating through the water, the chemicals and biological changes in ponds can cause mass fish deaths.

Low levels of dissolved oxygen is the most common natural death for fish. While most fish deaths are natural, biologists can’t rule out other causes such as pollution until tests are done.

Some fishers may be able to detect ponds with low dissolved oxygen levels. When ice fishers drill through the ice, the smell of rotten eggs or dying shiners are an indicator of low levels. However, these smells are natural. The rotten egg smell is hydrogen sulfide gas which occurs when there are low levels of dissolved oxygen. Oxygen levels in bodies of water return to normal once the ice melts in the spring.

If you find any dead fish in the winter, you are asked to report it to Environmental Police at 1-800-632-8075. MassWildlife biologists will then review each case and determine whether they are natural deaths or if further investigation is needed.