Oak Hammock Marsh
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Oak Hammock Marsh consists of approximately 20 square kilometres of open marsh, and a slightly smaller area of surrounding woods and grasslands. It is located approximately 20km north and slightly west of the northern suburbs of Winnipeg, Manitoba, near the town of Stonewall, Manitoba, centered near coordinates 50° 11' N, 97° 07' W.
The marsh is a remnant of an originally 47 square kilometre 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 bog underwent drainage for agricultural purposes beginning in 1897, and by the early 1960s, all but 250ha had been drained. Measures to restore a portion of the bog 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, 3450ha of marshland and marginal agricultural land had been purchased and 22km of dykes built to trap and hold water in three dyke-separated 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 control structures, water supply works, more nesting islands, additional dykes, and create a fourth compartment.
Water levels in the marsh are carefully controlled. It is common during wet years (when waterfowl have an abundance of alternative nesting sites) 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.
Not all of the adjacent purchased land has been allowed to grow wild. Cereal grain crops are planted in some of it, but never harvested, in order to supply migrating waterfowl with an autumn food supply while reducing crop predation pressure on local farms.
The marsh is therefore not a natural one, but is instead a constructed and managed wetland, designed for the creation of a waterfowl breeding and migratory habitat.
Critics say that this makes the marsh simply a "duck factory" for the benefit of hunters. Indeed, hunters have traditionally been a major source of revenue for Ducks Unlimited, who manage the marsh. However, supporters contend 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. And Oak Hammock Marsh supports many, many wildlife species besides game birds, as do all healthy prairie wetlands.
The marsh itself is closed to hunting, but game birds (primarily mallard ducks and Canada geese) are hunted in the autumn when they leave the marsh to feed in the surrounding grain fields. Hunting contributes in a significant way to the local economy, both in the money spent by the hunters and in the reduction of crop losses by the local farmers. Nor is it considered to be detrimental to the game birds themselves, as some hunting pressure keeps the flocks scattered and feeding over a larger area and therefore reduces the risk of disease epidemics.
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 center for the marsh. Boardwalks from the interpretive center allow public access to the marsh and dykes. The building of a head office and public facility so close to critical wildlife 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 (the building's roof is now a popular nesting site).
Oak Hammock Marsh is listed as a Wetland of International Importance under the Ramsar Convention.
