Obviously, no two lakes are exactly alike. Broadly, though, all can be classified into one of three environmental age groups: Oligotrophic (young, in geologic terms), mesotrophic (middle-aged), and eutrophic (old). Factors like predator-prey relationships, the amounts and types of aquatic vegetation, and many other structural considerations, help to determine the basic lake classification. This helps you decide where crappies should be located during each Calendar Period.

No matter where your favorite lake is located, it’s changing. In some waters, observable change may take centuries. In others, due to siltation caused by construction, logging, natural disasters, or any of a number of factors, change occur in only a few years. This aging process is often called eutrophication, and all lakes pass through it. A lake grows older not only in time, but in condition. The initial stages of eutrophication may take thousands of years. The final stages may happen quickly, especially with the intervention of man.

Throughout this process, the lake environment—structural makeup, food chains, vegetation levels, and dominant fish species—changes. Eutrophication brought on by human activity is primarily due to our rapidly increasing population. Waste disposal, fertilizer runoff from lawns and golf courses, removal of vegetation bordering the water—all these things and many more speed up the eutrophication process. Within a generation, humans cause changes that would take nature hundreds of years to effect. Each individual living on the shoreline accepts some responsibility for this, along with neighboring municipalities, industries, and agriculture. Laws restricting human activity along waterways have increased for decades.

Because of the manmade changes on most North American lakes, we classify them according to environmental condition rather than chronological age. Each category is a point of reference, making it easier to recognize similarities between various bodies of water. This, in turn, makes it easier to transfer patterns of fishing from one body of water to the next. The logical process for fine-tuning those patterns to meet the demands of each specific environment becomes easier to follow, too. Soon it becomes second nature to pursue patterns for catching crappies based on experience on other waters in the same category.