FWP News: Arapooish Pond experiences winter fish-kill
By angelamontana

Posted: April 25, 2023

Low dissolved oxygen levels from prolonged ice and snow cause event

BILLINGS – Arapooish Pond, also known as Koyama’s Pond, near Hardin experienced a fish-kill event this winter. FWP crews have surveyed the pond and are aware of the situation. Although there is a windmill aeration system at Arapooish Pond, there is no guarantee that it will prevent a winter kill event, especially during harder winters.

Fish, like humans, need oxygen to survive. While humans use their lungs, fish use their gills—made of fine, hair-like blood vessels—to absorb dissolved oxygen (DO) from the water into their bloodstream. If DO levels in a waterbody decrease enough, there is a potential for a fish-kill event.

Oxygen and other atmospheric gases dissolve into open water. Flowing water, such as rivers and streams, has higher levels of DO than standing water like ponds and lakes. The increased turbulence, or mixing of air and water, in faster-flowing waterbodies incorporates more oxygen from the air into the water. Aquatic plants provide DO in waterbodies through the process of photosynthesis. Plants take in carbon dioxide and release oxygen as a by-product, the exact opposite of the respiration process for animals.

During especially cold and snowy winters such as this year, prolonged ice and snow cover on lakes and ponds can lead to decreased levels of DO. Aquatic plants are not able to photosynthesize due to a lack of sunlight, and atmospheric oxygen is not able to mix with surface water. This reduction of DO can lead to decreased health in local fish populations, and potential large mortality events.

This is the case for Arapooish Pond. Species affected include common carp, a non-native and nongame species; largemouth bass, a non-native game species; and bigmouth buffalo, a native nongame species. Though a significant number of fish died, it is unlikely all fish in the pond were lost. FWP crews plan on conducting fish surveys this spring to better assess the condition of the fishery, pond and windmill aeration system and restocking needs.

Please call your local FWP office if you find a potential fish-kill site.

Photo: Arapooish Pond experienced a winter fish-kill event. Species affected include common carp, largemouth bass, and bigmouth buffalo. FWP photo.
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