In reservoirs and natural lakes, most of the bass population will be on the main body of water, as opposed to tributary arms. They will be relating strongly to vertical and fast sloping structure: rock bluffs, river channel dropoffs, standing timber, 45-degree rock or earthen banks, or standing timber. These are all places where they can make a major depth change by moving up or down: In cold water, bass are lethargic, and won't swim long distances to change depths. In clear lakes, bass often suspend in the water column rather than hold tight to cover.
Water clarity is a major determinant of bass depth in winter. In clear lakes, bass can go extremely deep — 50 to 60 feet is not uncommon. In murky lakes, they'll be much shallower.
Since bass are sluggish, I'll use a slow presentation. In any season, I use search lures to find active bass. In winter, I prefer ones that draw strikes without moving fast. Suspending jerkbaits are my favorite winter artificials, if the water clarity is sufficient to use them (these lures don't work as well in very stained water). The fact that you can fish these lures in the same place for long periods of time makes them extremely deadly on suspending bass. Leadhead grubs also work great now; they probe vertical and fast sloping structure efficiently. The same goes for jigs, metal blade baits and spoons. I may fish a crankbait in the upper end of the winter temperature spectrum.
While searching out likely bass holding areas, I'll fish parallel to the structure; this keeps my lure deeper in the water column longer.
This generalized winter pattern applies to natural lakes and all reservoirs, but in rivers, it's important to fish areas with no current. A big hole in the river bottom, where current washes overhead, is a good spot for smallmouth. Largemouth like backwater areas with some depth to them, like close to a marina.
Bass begin moving from their deep winter haunts toward their eventual spawning areas. I fish the same type of vertical areas now as in winter, but they should be close to a flat area, because bass like to spawn on flat places in protected water. If I had been fishing bluffs in winter, I would now fish the ends of the bluffs, close to some shallower water.
Northern banks are very important now because they're warmer than other areas on the lake. Avoid places hit by cold north winds.
Once the water hits 50 degrees, bass are definitely in a prespawn mode. Migration routes are important now in lakes and reservoirs. Bass will follow ditches, depth contours, tapering points and fallen trees on sloping banks toward shallower water.
If there's some stain to the water, a deep running crawfish pattern crankbait rooted along the bottom is strong now; bass feed heavily on crawfish emerging from hibernation during the late winter/early spring transition period. A slow rolled spinnerbait also works well. For combing large expanses of water, I love a lipless rattling crankbait like the Strike King Red Eye Shad, and I'll use this faster moving lure in the upper ranges of the prespawn temperature zone. I'll also continue to use a suspending jerkbait in clear water. Bass relate to cover such as stumps strongly now, especially in murky lakes; a jig-and-pig rules here.
I pick up my fishing pace considerably as the water hits around 52 degrees, and I may run down a bank while quickly throwing a Red Eye Shad or spinnerbait, then pause to pitch a jig when I come to a submerged log or brushpile.
Many bass will now be on flat, protected structure. Large expanses of shallow water are critical (10 feet or less on a lowland reservoir or natural lake, 8 to 20 feet deep on a highland reservoir). Look for areas on a contour map where the lines are spread far apart, not close together.
Not all bass spawn at once. Many will move onto their spawning beds around the new or full moon, or when the sun comes out after a long period of cloudy weather. At the same time many bass are spawning, others will be in a pre- or postspawn mode. Normally, the biggest bass are the first to spawn. You need to make a decision now as to which group of fish you'll target, because different approaches are required for each. Personally, I like to stay with prespawn bass as long as I can, because they're more aggressive and they'll weigh more.