The Wetlands of the United States was published in 1959 by the U.S. Fish and Wildlife Service and is commonly referred to as "Circular 39." The Circular 39 Classification System was the first method that the U.S. Fish and Wildlife Service used to classify wetland basins in the U.S. It is composed of 20 wetland types of which eight are found in Minnesota.
The Circular 39 classification was inconsistently applied among regions primarily because of a lack of detail in the definitions of wetland types. In 1975 the U.S. Fish and Wildlife Service developed a new classification that would serve as the basis of the new National Wetlands Inventory.
Minnesota Wetland Types
The eight wetland types found in Minnesota are:
Type 1: Seasonally Flooded Basin, Floodplain Forest
Type 2: Wet Meadow, Fresh Wet Meadow, Wet To Wet-Mesic Prairie, Sedge Meadow, And Calcareous Fen
Type 3: Shallow Marsh
Type 4: Deep Marsh
Type 5: Shallow Open Water
Type 6: Shrub Swamp; Shrub Carr, Alder Thicket
Type 7: Wooded Swamps; Hardwood Swamp, Coniferous Swamp
Type 8: Bogs; Coniferous Bogs, Open Bogs
A detailed description of each wetland type can be viewed on the Minnesota Wetland Types