What happens to fish in the winter?

Ice fishing for Northern Pike.

Fish inhabit Adirondack lakes and ponds year-round, with some of the best fishing opportunities occurring during the winter months. To understand fish behavior in winter, we must first consider the water conditions. 

If you've spent time on or near the water, you may have noticed that the temperature isn't uniform throughout the depth of the lake. This variation, primarily due to sunlight penetration, leads to distinct temperature layers, a phenomenon known as thermal stratification. Lake turnover, the process that redistributes water temperature and dissolved oxygen, occurs because water is densest at 4°C (39°F). In the fall, as surface waters cool, they become denser and mix with deeper water, equalizing the lake's temperature. Winds further facilitate turnover, distributing oxygen and benefiting aquatic life. 

During the summer months, when lakes are thermally stratified, cold-water fish such as Brook Trout (Salvelinus fontinalis) and Lake Trout (Salvelinus namaycush) seek the cooler, deeper waters of the hypolimnion, the bottom layer of the lake. However, oxygen levels can become depleted in this layer due to reduced mixing with surface waters and naturally occurring decomposition. These cold-water species are then pushed into layers where the temperature and oxygen levels are just right, between 10°C and 12°C (50°F and 54°F). 

In the winter, the temperature of lakes and ponds becomes more uniform, around 4°C (39°F). In shallower lakes and ponds, oxygen can still be a concern, as there is no replenishment from the atmosphere, especially when the water is frozen over. 

To survive during the winter months, fish have unique adaptations. One key adaptation is a slowed metabolism due to the colder temperatures. This leads to reduced activity and feeding rates, with fish staying in waters where conditions are more stable. With fewer food sources such as macroinvertebrates, flying insects, or zooplankton available, this strategy is essential. Fish also move less during the winter months to conserve energy, as it takes effort to cover distances in the water column. During this time, there is a higher mortality rate as fish struggle to maintain sufficient food intake without depleting their fat reserves. This is especially noticeable among smaller and younger fish, which haven’t had the opportunity to build their fat or energy stores. 

With these slower metabolism rates, fish may be more interested in your lure if you’re fishing. If you practice catch and release, consider the amount of time the fish is out of the water after the catch. Given their already lower energy levels, minimizing the time fish spend out of water increases their chances of surviving when released back into the water. Winter can provide a wonderful time to fish for species such as Northern Pike, Walleye, Lake Trout, and landlocked Atlantic Salmon.