The arrival of winter does not mean you can ignore your pond. Properly constructed ponds seldom freeze deep enough to harm fish because aquatic plants, especially the microscopic plants, continue to produce oxygen as long as light penetrates the ice. However, snow blanketing the ice prevents this light penetration, and plants can no longer produce oxygen. When this situation exists and the decomposition of dead vegetation uses some of the available dissolved oxygen, there may be insufficient oxygen for fish, and they may suffocate. Removal of snow from at least one-tenth of the pond surface will greatly reduce the likelihood of this happening. Good weed control during the growing season and operation of an aerator in the pond during the winter also will reduce this hazard.