Mid-field waterless depressions are some of the most common and important elements of the agricultural landscape on the Wełtyń Plain (NW Poland). In 1995–2000, in the northern part of the plain, research was conducted in 68 small, mid-field depressions with the water table below the soil surface. The aims of this study were: (1) to determine the floristic and phytosociological characteristics of this area, (2) to assess site moisture content on the basis of species composition, (3) to identify major environmental threats, and (4) to evaluate environmental diversity. The 10 recorded grass communities included mostly meadow and marsh vegetation, while nitrophilous and shrub communities were sporadic. The most humid of the studied depressions were covered by marsh communities, and their flora was the most valuable. The major threat to hydrophilous grass communities was their devastation.