Temporal bioassessment trends. The background colours indicate the local ‘ecosystem health’ according to Oberdorff et al. (2002). The line and the dots indicate the annual median fish-based index (FBI) across lowland sites in mainland France (n=326 sites under 500m in altitude, sampled at least 10 years with a first survey before 2004 and a last survey after 2017). The shaded area indicates the interquartile range.