Anthropogenic activities are in great concern with metal pollution in fluvial ecosystems. Metals are persistence and bioacumulable contaminants with severe effects on biota. From this perspective, the main aim of this study was to evaluate metal toxicity in the Riou Mort and Osor rives by using different Chl-a fluorescence parameters as a complement to the diatom community composition. Two independent experiments were carried out. Spring 2008, in the Riou Mort (France), which presents high Zn and Cd concentrations in water (Morin et al. 2007), biofilms were translocated from non polluted site to two metal polluted sites,and, after 6 and 24h Chl-a fluorescence parameters where evaluated by PhytoPAM: Spring 2009, in the Osor River (Spain), with a Zn historically contamination (ACA). biofilms were colonized on substrata and translocated from non polluted site to 5 different sites with different Zn concentrations in water. Samples were taken after 6 and 72 hours as well after 1, 3 and 5 weeks of exposure for Chl-a fluorescence measurements and taxonomical diatom analyses. The experimental design applied, by the use of biofilm translocations seems to be a good approach to evaluate in field acute and chronic metal effects on biofilm. The use of Chl-a fluorescence parameters on biofilm for assessing metal contamination on Riou Mort stream and Osor River revelead that this parameters are not specific of metal pollution and their sensitivity to detect metal pollution on biofilms adapted to metal pollution seems to be small. On the other hand, photosynthetic and quenching parameters responded quickly after acute metal exposure. The the diatom community composition seems to be a very sensitive biomarker of chronic Zn exposure, suporting its use for metal assessment.