Marshes in the Sanjiang Plain of Northeast China have undergone dramatic loss and fragmentation over the past decades. This paper analyzed the loss and fragmentation of these marshes for the period 1954-2005 using historical land-cover information and remote sensing data. In 1954, marshes covered one-third of the total land area but have decreased by 77% over the 50 year period. Results showed two distinct periods of impact: 1954-1986 and 1987-2005. In the earlier period, the number of marsh patches fell from 4,799 to 1,476 (-69.2%), and total marsh area decreased from 35,270 km(2) to 13,893 km(2) (-60.6%). In the latter period, the number of marshes declined from 1,476 to 1,037 (-29.7%), and the total area decreased from 13,893 km(2) to 8,100 km(2) (-41.7%). The rapid decrease in the number and area of marshes during 1954-1986 was largely attributed to extensive agricultural reclamation under the "Food First" agricultural policy. This resulted in many negative ecological consequences. In contrast, the slower reduction of marsh areas during 1987-2005 was due to the implementation of governmental policies for protecting and restoring marshes. Increasing air temperature would otherwise have enhanced crop yields and stimulated the conversion of marsh into crops.