Oxygen levels in a lot of backwater areas are extremely low. This can work to your advantage in that if you can work a deeper hole with some timber or even the slightest bit of flow, it should hold fish. Otherwise I’d be out in the river.
For bluegills I’d sit on wingdams. There are some good reports from local guys of big bull gills on wingdams with crawlers. Try to find the first dam in a series with this low flow.
For perch, they really seem to roam in the summer (or at least schools with jumbos). I’d bet I’ve caught more on cranks and leadcore than any other way from July-August. If you find them off the main breaks on Lake Pepin, the schools can be hundreds of fish.
Crappies are far from my specialty. We will catch a stray one here and there, but most have been caught in backwater areas with considerable depth and some timber. Their feeding windows seem to be extremely short this time of the year… mainly because there’s forage everywhere and they can afford to be picky.