# The Biological Assessment and Rehabilitation of the World's Rivers: An Overview
## 2 Biological Assessment of Rivers
### Europe  
In the European Union (EU), the Water Framework Directive (WFD) [16] is an umbrella for establishing ecological assessment programs in its 27 member-states. The WFD considers water a patrimony that should be protected for future generations and that all European water bodies should be recovered to Good ecological status (now by 2027). To achieve that aim it proposes a complex plan that includes catchment characterization, establishing water body types and delineating programs of measures to protect and recover the ecological status of water bodies. The novelty of the WFD compared to previous legislation is that ecological assessment focuses primarily on the conservation of aquatic assemblages whereas water physico-chemical characteristics and hydomorphology are considered supporting elements. In rivers the compulsory biological quality elements are benthic macroinvertebrates, fish and aquatic plants, usually divided into the diatoms (microalgae) and macrophytes. Finally, natural water bodies must be classified into 1 of 5 Ecological Quality Status (EQS) classes: High, Good, Moderate, Poor or Bad. This status (or ecological potential in the case of artificial or heavily modified water bodies) is obtained through the combined classificationsof biological elements with water chemistry and hydromorphology (usually based on the one-out all-out approach). Good status is the minimum acceptable quality that does not require measures for its improvement and where the biological elements deviate only slightly from near-natural reference conditions [152]. Before the implementation of the WFD, a diversity of indices existed such as: the BMWP and IBMWP, ASPT, BBI (Belgium Biotic Index) [153; 154; 155] or predictive models (e.g., [156; 157]) based on macroinvertebrates; the TDI (Trophic Diatom Index), IPS (Indice de Polluosensibilite Specifique), CEE (European Economic Community Index), IBD, GDI (Generic Diatom Index) for diatoms [158; 159; 160]; and the IBI and derived indices for fish [14; 15; 16]. Macrophytes were assessed with the IBMR, MTR (Mean Trophic Rank) and RVI (Riparian Vegetation Index) [161; 162; 163; 164]. After the WFD, the index values had to correspond to deviations from reference conditions that were established for each river type and that needed to be comparable across the EU [165; 166]. Sampling and analytical methods had to be compliant with guidelines such as, addressing the composition and abundance of biological elements, fish age structure, and quality classes that correspond to similar disturbance levels. This generated an exponential development of new methods for the biological assessment of rivers [17; 167; 168]. Finally, the assessment methods had to go through an Intercalibration Exercise (IC) that aimed to guarantee the comparability of classifications among MS [169; 167; 170; 168; 167; 169; 171; 172; 173]. This exercise was undertaken in groups of countries with similar types of rivers, the Geographic Intercalibration Groups (GIGs), such as the Northern, Alpine, Central Baltic, Eastern Continental and Mediterranean [167; 174; 175]. As a result of the IC process, many official methods adopted for macroinvertebrates by member states became structurally similar [175; 176]. Most countries adopted a multimetric approach, such as Italy (STAR_ICMI--Intercalibration Common Metric index), Portugal (IPtI--Indice Portuguese de Invertebrados), Spain (IMMi--Iberian Mediterranean Multimetric index), Ireland (MacrOper), Germany (Perlodes), Belgium (MMIF--Multimetric Macroinvertebrate Index Flanders), Austria, Sweden (DJ index) [177; 168; 176; 178; 179]. Yet, other approaches still coexist such as the biotic indices IBGN for France and the Iberian BMWP in Spain, and predictive models (RIVPACS--River Invertebrate Prediction and Classification System /RICT--River Invertebrates Classification Tool) in the UK [176].