Winter is a trying time for all wildlife with fish being no exception; feeding slows, egg/milt production starts, and the long wait for spring breeding begins. As fish metabolisms lower and pond activity lessens, oxygen availability becomes the main focus. The primary source of dissolved oxygen, even during winter, arises from photosynthesis thanks to phytoplankton, algae and submerged plants. Since sunlight is needed for photosynthesis; thick snow accumulation on ice for extended periods of time can result in a winter fish kill. Some simple tricks to help avoid a fish kill this winter include: inspecting inflows to ensure a supply of fresh water, shoveling snow off a portion of the ice to allow sunlight penetration (when ice is safe to traverse) and utilizing aeration systems or other instruments that keep a section of the pond ice-free. While winter fish kill can pose a serious threat, there is a plethora of factors that come into play and every pond is unique in how it functions and reacts in cold weather.