This European Standard gives guidance on procedures for the pro-rata Multi-Habitat-Sampling (MHS) of benthic macro-invertebrates in wadeable rivers and streams. The term "pro-rata" reflects the intention to sample adequate proportions of riverine habitats with reference to their percentage occurrence. The pro-rata MHS technique does not replace other techniques, but is rather, alongside other applications, a fundamental requisite of some multi-metric assessment approaches used to evaluate the ecological status of running waters. The method described in this document is one of the possible techniques among the existing pro-rata MHS techniques. The MHS methodology is based on Rapid Bioassessment Protocols , the procedures of the Environment Agency for England and Wales , the Austrian Guidelines for the Assessment of the Saprobiological Water Quality of Rivers and Streams , the AQEM sampling manual , the AQEM & STAR site protocol , EN 27828, the Austrian Standards M 6232 and M 6119-2 , , the German Standard DIN 38410-1  and the French Standard XP T90-333 . This European Standard also describes in a detailed manner how to sample different habitats that might be suitable for sampling approaches other than Multi-Habitat-Sampling.