Management of water-bodies affected by prolific growths of plants pose several problems related to assessment of created imbalances. The intensity of these phenomena should be considered on both spatial and temporal scales, as well as the impact of negative effects on practical uses of the water-bodies by man. An examination of invading growths recorded on the French hydrographic system has been carried out. As a result, an inventory of the most relevant plants was produced, called "risk species" belonging to different macrophyte groups like macro-algae, native hydrophyte phanerogams as Ranunculus sp., Potamogeton sp., Myriophyllum sp., Ceratophyllum sp., Lemna sp., and introduced phanerogams like Elodea sp., Lagarosiphon sp., Ludwigia sp., Myriophyllum aquaticum. Some helophyte plants, Cyanobacteria and two riparian introduced species (Fallopia japonica and Impatiens glandulifera), have also been considered. Biological strategies determine their proliferation potential by developing high growth and substantial propagation abilities, through some special morphological and physiological features and means of reproduction. Environment types and factors favour this capacity. These favourable environments are connected with environmental conditions such as high irradiation, mostly linked to shallow depth and water warming, stable or low hydrological conditions, high mineralization and trophic level. The occurrence of dense vegetation is usually the combination of these two aspects, with the influence of mostly several favourable factors. Some situations of minimal and maximal risks can be defined. This knowledge should improve understanding of these events and provide more information for management and control practices.