Sometime this month, in reservoirs across the Southeast, largemouth bass will make a major move from the deep places where they’ve spent the summer out on the main body of many lakes back into the tributary creeks.

That transition is triggered by the movement of baitfish, including blueback herring, threadfin and gizzard shad into creeks along channels.

But, as fishermen soon realize, all creeks aren’t created equal in the fall. Tributaries that hold a lot of spawning fish in the spring aren’t necessarily desired destinations in the fall.

So if your home reservoir has a half dozen or so major tributary creeks, how do you decide where to concentrate your limited days on the water?

Bass fishermen like Rick Morris of Bracy, Va. — a five-time Bassmaster Classic qualifier who has moved home to guide on Lake Gaston, a 20,000-acre reservoir on the North Carolina-Virginia border — know it’s a matter of understanding which features the best fall creeks will share.

“I look at the largest creeks on a lake, because they have more volume and more creeks, and they usually have a longer, winding channel with more bends that give you points and breaks — more structure for fish to hold on,” said Morris (www.rpmcustomrods.com). “They’ll hold more fish than a creek with a channel that just goes back straight with no bends or swings.

“Plus, they’re always pulling water through them, so you get more current, and the water quality is the best it is on the whole lake.”

And when bass that lounged on the main lake all summer move into these tributaries, they join fish that never left.

“The bigger creeks will usually have a lot of resident fish — all of them don’t live out on the main river,” Morris said. “During the summer, they’ll be around bait in the deepest part of the creek, around the mouth.”

When the transition happens varies, depending on the weather.

“September is still the tail end of summer. As the fall progresses, the bait moves back, and the bass come with them,” Morris said. “It happens fast. The first cool weather will move bait back.”

When baitfish point their noses upstream in the fall, the presence of current can draw them toward certain creeks or the river section of the lake. Current moving through a dam at the upstream end of a reservoir will draw bait and bass toward the tailrace, while water being pulled through the dam on the lower end that impounds a reservoir will set up current that pulls water out of creeks.

The more water coming out of a creek, the more likely baitfish are to head in that direction.

In most reservoirs, according to Morris, sharp creek-channel drops, especially on the outside bends of channels, will draw baitfish and bass because they can move back in creeks and from deep to shallow at the same time.

So the presence of sharp drops and flats that butt up against creek channels are bait and bass magnets.

“In a good, fall creek, you can fish deep banks on channels, banks closer to deep water,” Morris said. “In a good creek, the fish can move up the creek and out of the channel.

“A bass can cruise at 3 mph, so it doesn’t take him long to get somewhere, and that’s why a good, defined creek channel helps.”

There is one big exception, Morris admits.

On lakes with relatively small populations of herring or shad, where bluegill or other sunfish species make up a bigger part of predators’ diets, look for creeks that have plenty of pockets where bream spawn.

“I believe a lack of shad in a lake affects where bass go,” Morris said. “There aren’t as many shad in Gaston, not like the Tennessee Valley lakes, so bass concentrate more on bluegills; they’ll be around bluegill beds back in the pockets (in late summer).

“So you look for creeks that have a lot of pockets like that, with a lot of docks.”