Minnesota's 3.6 million ha of wetlands have been impacted by a variety of human activities, including agricultural drainage, urbanization, water control, and nonpoint source pollution. More than half of Minnesota's wetlands have been destroyed since the first European settlers arrived, an average loss of about 35,600 ha/yr. Drainage for agriculture is the major cause of wetland loss in Minnesota, particularly in southern Minnesota and the Red River Valley. In addition to impacting wetlands directly, wetland drainage affects downstream areas by increasing flood flows, and releasing sediment and nutrients. Urban development and highway construction affect a smaller proportion of Minnesota's wetlands, but substantially alter their physical, chemical, and biological properties. Hydrology has a major influence on the structure and function of wetlands, so changes in the frequency, duration, depth, and timing of wetland flooding can severely impact wetlands. While wetlands can assimilate low levels of sediment and nutrient enrichment, excessive inputs can be detrimental. Peat harvesting is not currently extensive in Minnesota, but could cause substantial impacts. Cumulative impact, the incremental impact of an action when added to other past, present, and reasonably forseeable future actions, is becoming an area of increasing concern.