river otters, which can be seen swimming in its numerous sloughs, ponds, and roadside ditches. In the fall, the Grizzly Island Wildlife Area herd of tule elk breeds. The bugling of bull elk can be heard especially in the early morning and evening. Access to certain areas of the Wildlife Area is limited during the first nine days of pheasant hunting season around November, and on Wednesdays and Saturdays during the waterfowl hunting season from October through January.</ref> Recent studies by the CALFED Suisun Marsh Levee Investigation demonstrate that the current configuration of the 230 miles of levees in the Marsh prevent salinity intrusion into the freshwater of the Delta used by 22 million people for drinking water. Flooded ponds As noted above, the dikes, or levees, of Suisun Marsh were originally built by nineteenth century farmers seeking to create farmland from tidal marsh. While this system is still in use on the Sacramento-San Joaquin Delta islands to the east, it failed in the Suisun Marsh due to unacceptably high soil salinities. Portions of the marsh were subsequently converted from farming to permanently and seasonally flooded wetlands in the twentieth century. Today, approximately 230 miles of levees maintain seasonally and permanently flooded wetlands. Between approximately mid-October and mid-January, managed seasonal wetlands are flooded to a depth of 8 to 12 inches to attract waterfowl. The rest of the year, the ponds are flooded and drained on a schedule designed to optimize conditions for plants which provide seeds preferred by waterfowl, namely alkali bulrush, fat hen, and brass buttons. Ponds left flooded through at least the spring provide brood rearing habitat. The flood-and-drain cycle is also designed to minimize soil salinity by leaching and flushing salts. Today, this flood management program also supports plants such as tules, cattails, saltgrass, and pickleweed, which may not yield preferred waterfowl food seeds, but do provide habitat for invertebrates important to pre-breeding waterfowl and other wildlife. When Suisun agricultural lands reverted to wetlands, they provided habitat for waterfowl displaced decades earlier by reclamation. In addition, the presence of these "new" wetlands eased waterfowl crop depredation in the Central Valley. It also provided habitat no longer available in the Central Valley due to extensive reclamation for agriculture and urbanization. By about 1930, waterfowl hunting had become the primary use of the Suisun Marsh. It is the dominant use today, with 158 private duck clubs and large