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Show gradient, water control is the primary means of managing vegetative growth and these wetlands have extensive, precise water control systems. One 3,346- acre duck club has 18 managed water levels, 88 water control structures, over 18 miles of channels and 21 miles of dikes. Precise water control is required to prevent avian botulism which can kill tens of thousands of birds, to minimize pond siltation and to control carp and other undesirable exotics. Water shortages cause damage and changes to vegetation and contribute to disease epidemics resulting in bird mortality. To maintain healthy marshlands, a flush of water is required to wash out toxins and provide salinity control during the spring. Critical issues for duck club managers include securing adequate water supply, delivery timing and reliability and maintaining water quality. Flooding issues are significant since these properties are located at low elevations near the lake and most owners or managers rebuilt after the 1980s flooding. Other pressing issues include access, road maintenance, predator control, trespass grazing and non- native plant species invasions which require ongoing control and expensive eradication. Important Island Habitat Areas In addition to established WMAs and privately managed habitats, the islands of GSL provide isolated habitat for a variety of colonial and migratory birds. The following table was used in the " Linking Communities, Wetlands and Migratory Birds" document to describe the islands of the lake, access and wildlife use ( Wetlands International, 1998). ( See Table 7.) 93 |