Two main criteria that directly affect the way bacteria perform in a pond are the water temperature and the amount of oxygen in the water. There are thousands of strains of bacteria that can be used for many different purposes. Bacteria are divided into three different categories; each category has specific water temperature ranges that they perform best in. Certain strains of bacteria will also perform differently depending on the amount of oxygen available in a pond.
Most products that contain bacteria fall within the mid range that will work best in water temperatures between 50°-115°F. Most mid range bacteria will still be actively working at temperatures as low as 34°F but on a much slower rate. If you are looking for a bacteria that performs in cooler water the packaging should market to that specific characteristic. Ideally, bacteria will perform best in warmer waters.