This study reports on the relationships between young-of-the-year (YOY) fish species richness and landscape and local factors in 20 backwaters of the Seine River floodplain. Using multiple linear regression, we tested the importance of three types of variable for explaining total species richness (TSR), phytophil species richness (PSR) and lithophil species richness (LSR): 1) colonisation-extinction processes, 2) habitat heterogeneity and 3) productivity. At the local scale, no variables describing habitat heterogeneity correlated with TSR, PSR or LSR. Productivity was correlated only with TSR according to a polynomial model. In contrast, variables relating to the colonisation-extinction process correlated with TSR, PSR and LSR: TSR varied mainly with backwater size, which is a surrogate of extinction whereas PSR and LSR correlated with the relative longitudinal position of backwaters and the size of their connection to the main channel. In conclusion, it seems that the total fish richness varies as a function of local factors whereas the components of fish diversity is rather influenced by landscape factors.