Large areas of irregularly flooded North Carolina salt marsh dominated by Juncus roemerianus were ditched in an attempt to control mosquito breeding. Comparative study of ditched and unditched marshes at three locations in N.C., was carried out to determine the extent of ecological changes. Ditches increase the area of aquatic habitat in marshes by a factor of 5, are inhabited by large numbers of juvenile fishes, crabs, and shrimp, and increase the amount of nursery ground for fish and crustaceans. Animal variety in ditches is low. Oysters planted in the ditches do not grow well. It is unlikely that oysters or shrimp could be cultured successfully on a commercial basis in ditches. Marshes were flooded 10-28% of the time. Fiddler crabs were present on all marshes. During flood tides fishes occur on both ditched and unditched marshes. Brushy vegetation invaded many spoil piles and along ditches. Invasion continued during the two year study. Failure of vegetation to significantly cover many spoil piles after eight years, and continuing erosion of spoil piles to form water-retaining levees along ditches is cause for concern.