Fish
(continued)
Sediment filling the river is damaging to fish populations because it physically removes habitat. For example, Lake Chautauqua lost 18.3% of its storage capacity in a period of less than 30 years. In 1975, areas in Quiver Lake were only a few inches deep during low-water stages, allowing willows to encroach on the lake. This further reduced habitat available for fish species.
The problem of sedimentation filling in the river and backwater lakes is particularly acute in times of low water combined with harsh winters. Much of the decline in sport fish abundance that occurred in the Illinois River after 1975 appears to be related to the winterkill during times of low flow in 1976-77 and 1978-79, and a summerkill in 1976. Until deepwater habitats are restored in the backwater areas outside of the navigation channels, it will be difficult have a sustainable sport fish population.
The fishery of the Illinois River face other problems. The plankton-eating Asian carp, including the bighead carp (Figure 46) and silver carp have invaded the river. They compete with the gizzard shad and other primary feeders of the river, which could result in reduced shad populations in the future. The Asian carp is known to leap from the water, sometimes landing in the boats of fishermen or researchers (Figure 47)!
The fishery of the Illinois River will continue to be affected by a host of invasive species because of its direct connection to international deep-water ports. International ships carry species of fish, mussels, and other organisms in their bilge water. As bilge water is emptied into waters connected to the Illinois River, the foreign species are released, and many colonize. This often has a direct, adverse impact to native fish species (Herndon 2002). Even with the threat of invasive species, however, the single biggest challenge to fish habitat in the Illinois River is the “constant and unabated rate of sedimentation” (Herndon 2002).
