Ice Life: A Look Under a Frozen Lake Champlain

When temperatures drop low enough to freeze wide stretches of Lake Champlain, the landscape takes on a new character. Ice replaces rolling waves, creating a surface that invites exploration—whether by skaters gliding across its glassy expanse or anglers setting up for the season. Beneath the frozen surface, life continues, with some species thriving in the cold while others slow down. The formation of lake ice is more than just a winter phenomenon—it shapes the ecosystem and the ways people interact with the lake during the colder months. 

The Behavior of Ice 

Water is both ordinary and utterly remarkable. This simple chemical compound, two hydrogen atoms bonded to a single oxygen atom, is unique in its behavior when frozen. Most substances increase in density when they transition from liquid to solid. But when water freezes, it expands and becomes less dense, allowing ice to float on top of liquid water.  

This single property of water is crucial for life on earth. While ice may seem like water’s harshest form, it insulates the water beneath, preventing it from freezing entirely. Water is densest at 4° C (about 39° F) and becomes less dense as temperatures drop toward freezing. In the winter, the warmest part of the lake is the bottom, where temperatures are more consistently around 4o C. 

If water was like other substances—becoming denser as it froze—ice would sink, and entire lakes could freeze solid from the bottom up. In colder regions like the Lake Champlain Basin, this would be catastrophic for aquatic life. With a maximum depth of 400 feet, the lake might never fully thaw in the spring, leaving its depths locked in ice year-round.  

Life on Ice 

Lucky for us—and for critters who call Lake Champlain home—ice floats. But how does life persist beneath and atop a frozen surface?  

Most animals experience winter as a time of reduced metabolism and slowed activity. The reason? A lack of energy from the sun. Shorter days and a lower sun angle reduce available light, limiting the growth of phytoplankton—the tiny, photosynthetic organisms that form the base of the lake’s food web. With fewer phytoplankton, zooplankton have less to feed on and populations also decline, creating a cascade that affects species up the food chain. 

Many fish retreat to deeper, relatively warmer waters to conserve energy. Their metabolism slows, and their bodies stiffen in the cold—much like how olive oil thickens in a refrigerator. While this is true for most fish in Lake Champlain, some species thrive under the ice. Burbot (Lota lota), lake trout (Salvelinus namaycush), and lake whitefish (Coregonus clupeaformis) remain active, taking advantage of sluggish prey. Lake whitefish even increase their fat stores, making the most of the season. 

Cold water fish are not the only animals in Lake Champlain who have icy vigor this time of year.  

River otters (Lutra canadensis) are year-round swimmers, undeterred by freezing waters. Their thick fur—up to 450,000 hairs packed per square inch—keeps them warm. An outer layer of coarse hair acts as a barrier, while a dense and soft undercoat traps insulating air. River otters produce hydrophobic oils that repel water, keeping their skin dry even when submerged.  

These playful creatures can be seen sliding across lake ice, a behavior that helps maintain their fur’s insulating properties, conserves energy by reducing friction, and, of course, is a fun way to strengthen social bonds. Humans are not the only species to enjoy skating on the lake in the winter! 

The Harsh Reality of an Icy Lake 

Of course, winter isn’t all fun and games. Survival can be brutal, and some creatures don’t make it to spring. 

One striking example is a winter fish kill, a grim consequence of prolonged ice and snow cover that prevents oxygen from replenishing in a lake. When this happens, fish suffocate beneath the frozen surface. According to the Vermont Department of Environmental Conservation, these die-offs occur during exceptionally cold, long winters.  

In recent years, winter fish kills in Lake Champlain affected invasive alewives (Alosa pseudoharengus). These small, silvery fish are native to marine environments and struggle with rapid temperature changes and extended periods of cold. First discovered in Lake Champlain in 2003, alewives suffered their first major die-off in 2008. Since then, mass fish kills have occurred every few years on the lake, with dead alewives washing ashore in early spring thaw—eerily preserved by the cold. 

Ice, Ice Safety 

Lake Champlain in winter offers an enticing landscape. But whenever you’re on ice, it’s vital to understand ice safety, whether you’re fishing, skating, or just taking a walk. Ice must be at least four inches thick to support an adult’s weight, even thicker for a car or snowmobile. New, clear ice is stronger than older, white, or cloudy ice, where freeze-thaw cycles may have weakened its structural integrity. Old, cloudy ice may need to be significantly thicker than clear ice to be safe.  

One way to test ice strength is with an ice testing pole—a long, heavy pole with a pointed end that allows you to jab the ice at an angle from a safe distance. This precaution helps minimize risk if the ice begins to crack. Remember that ice does not freeze uniformly, and a thin patch can exist right next to a thicker ice shelf. Moving water beneath the ice further weakens it, making areas near streams, bridges, culverts, and narrow waterways especially dangerous.  

No matter what, never go onto ice alone. Always inform someone of your plans and expected return time, and dress appropriately for the conditions, keeping extra warm clothes in a dry bag. And even if you’re just contemplating a brief stroll on ice, check out the ice fishing basics and safety tips on the Vermont Fish and Wildlife Department  or New York Department of Environmental Conservation website.  You’ll find information on how to stay warm, how to use an ice pick or ice claws to pull yourself out of the water, and how to test the ice for safety. You may be inspired to join the ranks of ice anglers yourself!   

Take time to experience Lake Champlain during this frozen season—without ever leaving the shore, you can listen to the ice shifting and creaking, breathe in the stark beauty of the landscape, and marvel at the resilience of the creatures that survive and even thrive in these extreme conditions.