Construction of the Mississippi River's lock and dam system was authorized in 1930. There are 29 locks and dams, although only 27 are shown on this map. The Upper St. Anthony's Falls and Lower St. Anthony Falls locks and dams are not shown, but are positioned upstream from Lock and Dam 1 in downtown Minneapolis. Three other interesting lock and dam facts: There is a Lock and Dam 5A between Lock and Dam 5 and Lock and Dam 6; there is no Lock & Dam 23; and the 26th lock and dam near St. Louis is named the Melvin Price Lock and Dam after a former U.S. Representative from the St. Louis area. All locks and dams were intended to maintain a 9-foot-deep main channel for commercial navigation.

The water behind a dam carries a pool name that matches the dam's number. For example, Pool 13 is created by Lock and Dam 13 just above Clinton, Iowa.

Generally speaking, the pools 13 north have more acres of backwater lakes and side channels. Water clarity is generally a little better on those pools, as well, enabling more widespread growth of aquatic vegetation such as lily pads, arrowhead, deer tongue, eel grass, various pondweed species, coontail, and duckweed. Smallmouth bass are also more plentiful to the north, although localized populations do exist further south. In recent years, both vegetation and smallmouth populations have slowly increased in pools in the southern half of the upper reach.

Every pool has a unique personality and an amazing variety of bass habitat. Some of the better pools, and those most popular with tournament organizations, are 4, 5, 7, 8, 9, 10, 13, and 19. Many tournaments with 5-fish limits require at least 14 to 16 pounds to win. The average bass weighed in a tournament is around 2.4 pounds.