The morphological response and distribution of Potamogeton pectinatus L., P. lucens L. and P. perfoliatus L. were investigated in relation to sediment and depth gradients within the littoral zone of Lake Geneva. Biomass, maximum shoot length, shoot biomass and biomass density were the plant traits analyzed, together with sediment characteristics: texture, water content, organic nitrogen and carbon, and exchangeable phosphorus and potassium. The relationships between (i) depth and sediment characteristics vs. species distribution and (ii) depth and sediment characteristics vs. plant traits were first studied. Regression models for the biomass and the shoot length of each species are proposed. These models are applied in st related article (Lehmann et al., 1997) in order to study the relationship between plant traits vs. species distribution through a Geographic Information System modeling. Besides the fact that P. pectinatus was more often found in sediments with higher organic content, no direct relationships were found between sediment characteristics and species distribution, Neither could the presence of patches of bare substrate be explained by differences in sediment characteristics. The effect of the sediment characteristics on plant growth showed in general a negative influence of organic matter content (except for P. pectinatus), and a positive influence of the fine texture and phosphorus, P. pectinatus grew better in shallower water, P. lucens appeared to have the best competitive abilities and P. perfoliatus performed best at deeper sites.