Locks and Dams
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. Raising the water level to enable navigation inundated thousands of acres of floodplain, creating an incredible diversity of habitat. Species better suited for lake-like habitat, such as largemouth bass and panfish, began to thrive.
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. Prolonged high-water events limit light penetration and can diminish aquatic vegetation beds, especially in main channel border and slough areas with current. There is also plenty of wood cover in the form of laydowns and stumps. When it comes to rock, natural limestone and gravel stream bed exists in some places, but rip-rap installed for bank stabilization along with wing and closing dams that direct current toward the main channel are more important as bass-holding structure.
Every pool has a unique personality and an amazing variety of bass habitat. Smallmouth bass are more plentiful to the north, although localized populations do exist further south. Bass populations are very strong in the upper pools, coinciding with the prevalence of good 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. And often, especially on the northern pools, five-fish limits are common. The average bass weighed in a tournament is around 2.4 pounds. Where the Upper Mississippi shines in numbers, it’s not the place to go for a trophy. River bass live a tough life, and a 5-pounder is a real prize. A 6+ is very rare occurrence. And a true 7 could be a river record.
The big river is an extremely fertile fishery. During most years, high water periods in the spring due to rain and snow melt enable good spawns and plenty of cover for fry to hide in. The biggest problem facing the Upper Mississippi River bass fishery is loss of overwintering habitat due to sedimentation of backwater areas. Radio telemetry studies have shown that centarchids — the family of fish including largemouth bass, bluegills, and crappies — have very specific requirements during the winter months for dissolved oxygen, current, and water temperature. Backwater lakes are essentially the only areas that can meet those requirements. As sediment introduced from the vast Mississippi River watershed settles into backwater areas, depth is lost. When winter ice cover is added, some backwater areas become too shallow to support overwintering fish. A second problem is the loss of islands, which is especially noticeable in the lower sections of many pools. Islands help break the current and slow wave action, creating more favorable conditions for the growth of aquatic vegetation.
In 1986, Congress authorized the Upper Mississippi River Restoration Program in Water Resources Development Act to help address ecological needs. This program includes Habitat Rehabilitation and Enhancement Projects (HREPs) and the Long Term Resource Monitoring (LTRM) program. HREPs and LTRM are designed to improve the environmental health of the Upper Mississippi River and was formerly known as the Environmental Management Program (EMP).
Many HREP projects have been completed and are planned in the future to combat the effects of the threats covered above. These projects are critical to the long-term health of this amazing fishery.