Danube, an old transporting way and the human activity are the main dispersal factor for diaspores of plants, like weeds and alien invasive plants. Some of these species have ornamental or horticultural origin, escaped from cultivation. Planting of the alien woods (Robinia pseudacacia, Populus x canadensis, and Juglans nigra) and decrease of the area occupied by original floodplain forests were the main-induced changes here. The character of the forests have been changed, plantations of introduced plants have became the focus for spreading synanthropic and invasive plants. At the present Impatiens glandulifera, Aster lanceolatus and Negundo aceroides are the species invading the moist floodplain forests (alliance Salicion albae) on the Danube most massively. Solidago gigantea, S. canadensis and Impatiens parviflora invade more dry, mesic forest type. Ailanthus altissima, Stenactis annua agg, Ambrosia artemisiifolia, Artemisia annua, Fallopia japonica, Helianthus tuberosus invade forests margins, ditches, forest roads and by-way. Water habitats of arms and canals are threatened by Elodea canadensis and E. nuttallii