Warm water gets re-aerated naturally during the fall turnover process. Now Camp Lake starts with oxygen from top to bottom and can get through winter without need for aeration again until spring. Musky may be stocked in waters that suffer winterkill no more than once in 15 years, and other species may be stocked in waters that suffer winterkill no more than once in 10 years. Kaas says fry are typically stocked in winterkill waters in the first year because they survive well in the absence of a lot of other fish, although mitigating circumstances may call for stocking larger fish known as fingerlings. If fry stocking is unsuccessful in that first year, fingerlings may be used the second year, he says.
Many biologists annually anticipate winterkills and submit quotas in the previous year.
When unanticipated winterkills occur, requests for fish are submitted as soon as possible after the winterkill occurs, are added to the statewide production plan at a higher priority, and the stocking will occur in that coming spring, Kaas says. The most consistent predictors of winterkills in lakes with no outlet and in ponds are depth and amount of organic matter, according to Simonson. Research has shown that frequent winterkill occurs in ponds less than 10 feet deep while winterkill is rare in ponds greater than 16 feet deep. Nongame species tend to be able to tolerate low oxygen levels better than game fish. Fish species tolerant of winterkill conditions include black bullheads, fathead minnows, and golden shiners, buffalo, carp, mudminnows, redbelly dace, blacknose shiners, backchin shiners, and Iowa darters, Simonson says.