The marsh is a remnant of an originally 470 sq km area of marsh and fen near the south-western corner of Lake Winnipeg. This larger marsh had the original English name of St. Andrews Bog. But the original wetland underwent drainage for agricultural purposes beginning in 1897, and by the early 1960s all but 60 ha had been drained. Measures to restore a portion of the wetland began in 1967 when the Governments of Manitoba and Canada embarked on a cooperative program with Ducks Unlimited Canada and other wildlife conservation organizations to restore marginal agricultural lands to a state suitable for wildlife. By 1974, 3,450 ha of land had been purchased and 22 km of dykes built to trap and hold water in three dyke-separated marsh compartments. In addition, 58 nesting islands were constructed within the three compartments. In 1984, the Manitoba government signed a further development agreement with Ducks Unlimited Canada to construct water control structures, water supply works, more nesting islands, additional dykes, and create a fourth compartment.
Management
The marsh is a re-constructed and managed wetland, designed for the creation of a waterfowl breeding and migratory habitat. Water levels in the marsh are carefully controlled. It is common during wet years for the water level in one or more of the compartments to be lowered for the summer, creating an extensive area of dried mudflats. This drying and later reflooding promotes the growth of emergent marsh plants such as bulrush and cattail, and therefore maintains the vegetation cover of the marsh; otherwise, the natural tendency would be for the marsh to become over several years simply a shallow lake, with a sharply defined shoreline and little nesting cover. Furthermore, not all of the adjacent purchased land has been allowed to grow wild. Cereal grain crops are planted in some of it, in order to supply migrating waterfowl with an autumn food supply while reducing crop losses on local farms.
Hunting
Critics contend that the marsh is simply a "duck factory" for the benefit of hunters. Supporters believe that it would be unrealistic to expect that the required funds to recreate the marsh would have been forthcoming if wild ducks had no economic and recreational value to sportsmen. Oak Hammock Marsh, like other prairie wetlands, supports many wildlife species besides game birds. The marsh itself is closed to hunting, but game birds are hunted in the autumn when they leave the marsh to feed in the surrounding grain fields. The waterfowl is additionally protected by a buffer zone extending 1 km from the water inside which hunting is prohibited, this protection extending outside of the WMA in some locations.
Ducks Unlimited Canada national office
The western shore of the marsh is home to Ducks Unlimited Canada's national head office, in a building that also serves as a public Interpretive Centre for the marsh. Boardwalks from the Interpretive Centre allow public access to the marsh and dykes. The building of a head office and public facility so close to criticalwildlife habitat was the cause of controversy in the 1980s. Opponents believed the traffic associated with the building would disturb the wildlife. These concerns have proven unfounded, as the wildlife have since grown quite accustomed to the building and its people.
