TEMPERATURE EDGES

Less obvious than physical edges are environmental edges like water temperature. Yet all fish are keenly sensitive to their surrounding medium and follow temperature gradients to find the best conditions for feeding, digesting, and resting. In winter, bass often move to areas that offer warmer water. Springs and tributary creeks bring in warmer water while power plants and industrial cooling ponds often bring steamy water into a river or impoundment.

Bass use their innate thermometers to occupy water that allows more active feeding but isn't so hot that it over-revs their metabolism. Excessive water temperature can quickly sap energy, making it difficult for a fish to consume enough food to remain healthy.

WATER COLOR EDGES

Black bass rely on vision for much of their feeding and generally thrive in water that's at least moderately clear. If a reservoir or river becomes muddy due to rain, feeding slows considerably. At times, murky water entering an impoundment will create a water-color edge, often called a mudline.

The mudline moves slowly downstream, creating a sharp edge where murky water adjoins clear water. The advancing murk pushes baitfish ahead of it, and this throng of prey attracts bass, wipers, stripers, and other fish to the feast. Predators lurk in the mixing water and readily attack baitfish. Bass seem to move down with the mudline as it drifts toward the lower end of the reservoir where it may dissipate, or color the whole lake.

CHEMICAL EDGES

Bass, however, aren't particular about water quality as are trout, shad, or walleyes, but they move where conditions are tolerable, avoiding water of poor quality. Key considerations are oxygen and pH.

Black bass favor water with a dissolved oxygen content of 6 parts per million or more and generally avoid water with less than 3 parts per million. Such water can occur toward the bottom of a pond, lake, or small impoundment that carries a considerable organic load. Decomposition in the bottom water lowers oxygen, and bass must move shallow. An oxygen meter will define such edges.

Deoxygenated water can also flow from a overly fertile tributary, such as one draining a heavily farmed watershed or one with hog farms. In densely vegetated areas, oxygen levels in the weeds can be low after a night of respiration and no photosynthesis. Low oxygen pushes bass to the edge at dawn. As photosynthesis commences, oxygen levels rise, and bass may reenter the mats of grass.

The pH level isn't often an important consideration, since few waters with bass have a pH reading lower than 6, although some Florida lakes are more acidic than that. A pH level lower than 5.5 may be harmful to bass. Where algae is dense, however, alkalinity can rise above the suitable level in hot sunny summer weather. Bass will avoid water with pH greater than 9.5. A pH meter reveals these breaks. Bass in water of poor quality often are inactive and uncatchable.