Big Grass Marsh is located just west of the town of Langruth in the Rural Municipalities of Lakeview and Westbourne, in south-central Manitoba. This site is also refered to as Langruth-Rural Municipality (RM) of Lakeview. It is a low-lying, flat area that consists of a large marsh, surrounded by community pastures and agricultural land. The marsh includes Jackfish, Seagull and Chandler lakes and is includes a variety of habitats: remnants of tall-grass prairie, wooded areas, willow scrub, and man-made drainage ditches and dykes. The marsh was drained between 1909 and 1916 for agricultural purposes, but the area was found to be unsuitable for agriculture. In 1938, Ducks Unlimited (DU) began their first restoration project in Canada here. A community pasture in Westbourne RM that began in 1941 meant that water levels in the Chandler Lake section of the marsh were lower then ideal for waterfowl. In the 1940s the marsh flooded at least once, a muskrat industry developed and the two RMs took control of the marsh as a profitable enterprise. The situation changed in the early 1950s and DU became the main manager after 1953.

During spring and fall migration, tens of thousands of ducks and geese, including Canada and Snow geese, regularly use Big Grass Marsh. As long ago as the 1940s, the Winnipeg Free Press carried articles on the tremendous numbers of geese that regularly pass through Big Grass Marsh, and some have described this area as one of the most important waterfowl staging areas on the continent. The area is less well known now, perhaps because of the popularity of Oak Hammock Marsh. As many as 200,000 migrating Snow Geese have used the area in spring and fall - this is about 7% of the Mid Continent population of Snow Geese. Canada Geese (Tall Grass Prairie and Eastern Prairie populations) are also abundant in both spring and fall. Thousands of puddle and bay ducks pass through or stay for longer to moult or stage. Mallards are the most common with over 10,000 occasionally reported. Included among the 16 other duck species found here are: Northern Pintail, Gadwall, Northern Shoveler, Redhead, Ruddy Duck and Ring-necked Duck. Many of the migrant ducks also breed at Big Grass Marsh. Most of the data for this site is over 20 years old, thus current waterfowl usage is uncertain.

Although half of all the Sandhill Cranes migrating through southern Manitoba each fall used to stop at Big Grass Marsh, the numbers have declined over the years, so that now cranes are thought to number in the hundreds, as compared to over 6,000 (1% of the present global population) in the early 1960s.

In the 1940s, at least 5,000 Franklins Gulls bred in the area, but their numbers have also decreased, since only 250 pairs were recorded at Jackfish Lake in 1977. A list compiled in 1971 showed that 73 species of birds bred in the area.

For many decades, the primary land uses in the area of Big Grass Marsh have been agriculture and cattle production. Water levels are thus lower than they were at the time of the earliest European settlement of the area. The marsh is still under some pressure from agricultural interests to convert or drain land. Consequently, the restoration of water levels to depths which are more productive for nesting waterbirds and other animals would be a difficult task. In the 1990s, however, DU helped convert flood prone cropland to forage and livestock grassland, which is better for birds than cropland and helps ease the pressure for lowering the lake levels. DU currently have a license to control water levels in part of the marsh.

The province recognizes that the area has wildlife value and tourism value: The Jack Fish Lake Nature which will include a self-guided nature walk is under development, and the Westlake Tourism Association will be promoting the area as an ecotourism destination. The Whitemud Watershed Conservation District, in conjunction with numerous groups, is in the process of finalizing a detailed management plan for Big Grass Marsh. Their aims include improving water regulation and using the marsh as a water storage area (to be controlled at the south end), thereby reducing the risk of flooding. Also, the area is a candidate Manitoba Heritage Marsh. The Canadian Wildlife Service bands Mallards here in the August.