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.

As a lake ages, its character changes. Environmentally young lakes are deep and clear, while older lakes are shallow and murky. Young lakes tend to be deep, cool, and oxygen rich, ideal for species like lake trout and whitefish, while crappies tend to run small but can be fairly populous though confined to bays and “lake-within-lake” scenarios. Old lakes are weed-choked and oxygen poor, supporting species like carp and bullhead, while crappies tend to be sparse but sometimes grow large. Between those two extremes lie the optimum lake environments for crappies—usually mid-mesotrophic to early eutrophic natural lakes. While it’s possible to have a weed-choked, late eutrophic lake produce crappies of good number and size, it’s the exception and not the rule.

The three basic categories of natural lakes can be subdivided further into early-, mid-, and late-stage, creating nine specific categories. First, however, let’s consider the three basic categories.

OLIGOTROPHIC LAKES

The youngest and least fertile lakes typically have rock basins and, since many were formed in the most recent Ice Age, are found almost exclusively within the northern latitudes of North America. Oligotrophic lakes have steep drop-offs, few weeds, and shorelines punctuated with conifers or surrounded by tundra. Big boulders and huge slabs of bedrock are common in the shallows. The nutrient level of the water is typically low, and oxygen is available at all depths. These lakes usually support only a few pounds of gamefish per acre and are most suitable to coldwater species like char, whitefish, and tulibee. Crappies most often appear in oligotrophic lakes during the later stages of this lake classification, and then only within bays or confined basins that more closely resemble mesotrophic or eutrophic environments.

MESOTROPHIC LAKES

Mesotrophic or middle-aged lakes typically have shorelines less gorgelike and drop-offs less steep than oligotrophic lakes, having less depth overall. Huge boulders and bedrock give way to smaller rocks with occasional boulders. Sand and gravel substrates are more apparent. Shallow flats appear, where direct sunlight contacts more bottom-area of the lake. Aquatic vegetation is usually abundant. Shoreline terrain is more varied and plant life more diverse. The water contains more nutrients. The lake is moderately fertile, the water characterized as “cool” overall, and many pounds of fish are present per acre. Mesotrophic lakes support a wider range of species than oligotrophic lakes. Crappies thrive in mesotrophic lakes.

EUTROPHIC LAKES

The oldest lakes, in geologic terms, tend to be warmwater environments. Shallow weedgrowth is thick where the water remains clear. In murky eutrophic lakes, weeds may be sparse, while clear ones often become weed-choked in summer. Lake bottoms consist of muck, marl, or clay—sediment that piled up in the lake’s basin over the millenia, filling in a formerly mesotrophic environment. Typically shallow flats are expansive, with gradual drop-offs that taper to the main basin—the bottom of the lake. Secondary drop-offs are rare and maximum depths are less than 40 feet. Marshes normally surround part or all of these lakes. Hardwood trees and flat shorelines are the rule.

Sometimes eutrophic lakes are called “dishpan lakes” because of their more uniform shape and shallow depth. Typically, these old lakes are the most fertile and have large fish populations. Crappies do well in early- to mid-stage eutrophic lakes, but become sparse in older, marshier lakes. In the far South, however, crappies fare well in bayous and many other shallow, marshy environments. In most parts of the country, as these lakes age, they begin to favor species like carp, bullheads, bowfin, and other species better suited to low-oxygen environments.