I hear anglers talk a lot about how a fish’s metabolism slows in cold water, that they eat infrequently or that it takes a slow presentation because the fish can’t swim fast.

That’s partly true, but have you ever wondered about the lake you are fishing (and where the fish live) and what all the other underwater life is doing when the water gets cold?

For starters, I’m talking about southern waters — lakes and ponds that don’t freeze over.

Throughout all except the southern counties of Mississippi, the water temperature drops to the mid-40s or low 50s. For lakes and ponds that were stratified in the summer, turnover has already occurred. The water temperature is generally the same, top to bottom.

If you are looking for warm water, look to shallow areas with good sun exposure, and downwind shorelines and pockets where the sun-warmed surface water will accumulate in the afternoon. These same areas, by the way, are likely to have the coldest water early in the morning after a cold, clear night.

The cold water affects everything. The phytoplankton — the algae suspended in the water that is the primary energy supply to the food web — will still be abundant but change to different species of algae that thrive in cool water.

The water might have a brownish color. Don’t be concerned. Often, lakes that had a greenish tint in the summer will be brownish or tan in the winter as the phytoplankton changes from the green algae to a group of algae called diatoms, also known as the golden or brown algae (not related to the golden algae that has caused fish kills in Texas and Southwest reservoirs).

Most rooted aquatic plants die. Areas in the backs of coves or pockets where dense stands of submerged weeds like hydrilla or southern naiad grew in the summer might be inhospitable to fish, as the decomposing plant material strips the oxygen from the water.

Obviously, the cover provided by the aquatic plants is gone, so the area loses its angler appeal. But it also might have lost its fish appeal. Aquatic plants provide ample surface area for attachment of aquatic invertebrates, like insects and crayfish, that feed invertebrate eaters like sunfish, which in turn are prey for bass. When the plants are gone, so is the food web that starts with invertebrates that live on the plants.

The forage base changes in winter. Aquatic insect larvae — like mayflies, dragonflies and midges — provide primary food for sunfish and small crappie and catfish. The adult insects emerge in the summer and lay eggs to complete their life cycle. The eggs hatch and the larvae grow. Aquatic insect larvae are abundant in the winter, but they are small compared to the size they will reach in early summer before they again emerge.

And many crayfish are in burrows, inactive and unavailable to fish.

Food, measured by weight or energy, is in short supply.

Food also is dwindling for larger fish eaters like bass, large crappie and catfish. Shad, the dominant forage fish in most Southern reservoirs, are increasingly scarce. Some are dying from the stress of cold water, and the smaller individuals are consumed by predators. Similarly, the small individuals of other forage fishes are depleted by predators.

There is a bright side to the change in forage supply: Larger shad, sunfish and other fishes that can be consumed by large bass and catfish remain relatively abundant, and can be easy prey for big bass and catfish.

Winter will end, the water will warm, and fish will resume active feeding to satisfy their increasing energy needs and to accumulate the energy needed to spawn.

That their food supply, particularly for those fish that rely on other fish for food, is at the annual low point might contribute to the high catch rates anglers typically enjoy in the spring.