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. 336 BIOLOGICAL REPoIn' 19 substrate, backwater insect production contrib- uted 19.30Al, and sand substrate production was 11.8%. By 1980, snag production dropped to 50.4% of total production, while backwater production contributed 14.8% and main channel sand bar 35.8% (Mestl and Hesse 1992). Based on total available habitat, snag insect production in one unchannelized reach (downstream from Gavins Point Dam) was down by 65% between 1963 and 1980 (Mestl and Hesse 1992). Recent observations in the unchannelized reach upstream from Gavins Point Dam indicate that the insect community is even less abundant than in the downstreani reach. We have not quantified production differences; however, we did quantify the amount of insect biomass drifting through both unchannelized sec- tions in 1984 (Hesse and Mestl 1985). Mean monthly invertebrate drift biomass was 83 kg in the upper unchannelized section and 376 kg in the lower unchannelized section, nearly 4.5 times greater. The changing relative abundance of fish in the Missouri River can most likely be explained by the changing availability of insects. For instance, flat- head chubs used mostly terrestrial insects, which fall into the river from woody debris protruding from the water or. along the bank, while plains minnows used the film. of diatoms and insects from accumulating soft sediments in quiet backwaters (Cross 1967). Overhanging trees and snagproduc- tion, and off-channel backwater production have been reduced so much that midchannel sandbar production has become a larger proportion of total system production. Flathead chubs and plains minnows have been replaced by emerald shiners (Notropis atherinoides), which feed primarily on zooplankton in higher-current sand substrates; insects are of secondary importance in their,diet (Fuchs 1967). Sauger do not compete well with sight-feeding predators such as northern pike (Esox lucius) and SlD.AlITnOUth bass (Micropterus dolomieu) foraging for emerald shiners in shallow, nonturbid bars and backwaters. We propose that large woody debris, brush, leaves, and grass should be returned to the Mis- souri River in large quantities. Such materials are available in communities near the river, and new legislation has banned yard waste from landf'ills in Nebraska beginning in 1994. Communities are exploring innovative environmental options for disposal of yard waste, and placing it in the Mis- souri River is a better way to use it than to bury it in overflowing landfills. Loss of Floodplain Connectivity The Missouri River had a wide (32 km) flood- plain, part of which was inundated each year. Welcomme (1985) found a direct relation between duration of floodplain inundation and standing stock of fish the, next year. Karr and Schlosser (1978) suggested that standing stock may decline by as much as 98% when the lateral linkage be- tween floodplain and channel is severed. Junk etal. (1989) proposed the flood pulse theory as a mechanism to maintain the essential linkage be- tween river channels and the floodplain. The Missouri River has been deprived of a flood- plain. More than 178 million ha of this essential habitat has been lost (Hesse and Schmulbach 1991). This habitat represented the off-channel area, where velocity was reduced and the bottom was muddy. Monis et al. (1968) determined that, as channelization occurred, 67% of the benthic insect production was lost in direct proportion to lost off-channel habitat. We recommend that federal mitigation projects be expanded to include the entire length of the remAining riverine sections. Project design should include the hydraulic reconnection of old cut-off sections of the erosion zone to the main river. Through acquisition in fee title or environmental easement, a publicly owned conidor should be created to provide at least a minimal floodplain. More than $100 million has been spent to build nearly 467 Ian of federal levees on both sides of the Missouri River from Sioux City, Iowa, to the mouth (Missouri Basin States Association 1985; Hesse 1987). These levees were designed to protect agrl- cultural lands on the floodplain landward of the levee. More than 10,000 ha of old erosion zone lie riverward of the levees in Nebraska. There should have been provision for the lands riverward of the levees to become part of a public conidor for the river's floodplain. Altered Hydrograph The precontrol Missouri River canied peak run- off during two periods, March-April and June (Hesse and Mestll993). Since 1954, dams on the mainstem and tributaries have eliminated the peaks and produced a flat, metered hydrograph, which has effected reproduction of native fish and aquatic insects (Hesse and Carlson 1992). More- over, before 1954, flushing flows, known as domi- nant discharge, occurred every 1.5 years. Mter