# The Biological Assessment and Rehabilitation of the World's Rivers: An Overview
## 2 Biological Assessment of Rivers
### Central and South America  
In South America, bioassessment is not homogeneous: there are countries with well-structured and consolidated monitoring programs based on chemical, physical and microbiological parameters (e.g., Brazil, Peru, and Uruguay); others have well-defined legal guidelines but no national initiative (e.g., [101; 102; 103; 104]); and others with no prospect for monitoring (e.g., Venezuela, Suriname, Guiana). However, there is no official national program that uses biological indicators in any South American nation (Table S1). In some countries, environmental impact assessment includes aquatic biota, with macroinvertebrates and fish being the most common (e.g., Ecuadorian normative for Mining Impact assessment). In a few cases, legislation on the use of biological indicators to assess rivers exists but is not applied by governments. One example is Costa Rica, which legislated the classification and evaluation of surface waters based on aquatic macroinvertebrates [105] and very recently the streams and riparian areas protection and conservation (Politica Nacional de Areas de Proteccion de Rios Quebecadas, Arroyos y Nacientes 2020). In Brazil, CONAMA Resolution 357 [106] focused on waters for human uses and supports the use of aquatic assemblages or organisms to assess water bodies and the importance of maintaining riparian vegetation to protect aquatic biodiversity and preserve ecosystem services. In the Brazilian state of Minas Gerais, Joint Normative Resolution COPAM/CERH-MG No. 1 [107], establishes that aquatic environments should be assessed by biological indicators, with the determination of reference areas, assessment methods and bioindicator groups, including fish and benthic invertebrates. Colombia also has guidelines for implementing standardized ecological monitoring of aquatic assemblages, in addition to an ecological quality index [108]. Nevertheless, in the last 20 years a considerable amount of information has been produced in South and Central America on the ecology, biodiversity and response of organisms to environmental stressors in rivers [108] such as in: Uruguay [109]; Paraguay [110]; Bolivia [111]; Chile [112]; Colombia [113]; Peru [114]; Ecuador [115]; Guiana Francesca [116]; Venezuela [117]; Brazil [118; 119]. Most studies were conducted based on a single or few temporal samplings with some exceptions covering multiple years, such as in studies of the Rio das Velhas basin, Minas Gerais, Brazil [120; 121]. Several countries follow the reference condition approach (e.g., [111; 114]--Bolivia; [115]--Ecuador and Peru, [122]--Brazil; [112]--Chile). In the Brazilian neotropical savanna and Atlantic Forest biomes, the establishment of reference conditions for ecoregions have also been investigated [123; 124], respectively. Additionally, over time a variety of biological indices have been applied and adapted for macroinvertebrate assemblages: BMWP ([125]--Brazil; [113]--Colombia; [126]--Bolivia, [115]--Ecuador and Peru); taxonomic richness [122; 127], EPT richness [128] and Saprobiotic index [129]. However, over the past decade, there has been a convergence on the use of MMIs using various characteristics of macroinvertebrate and fish assemblages (e.g., [122; 130; 131; 132; 133]), and predictive models [134; 135; 136]. Some studies also follow trait-based approaches for assessing neotropical rivers (e.g., [135; 136; 137; 138; 139; 140; 141]). Non-native and invasive species have also been used as bioindicators in the reservoirs of hydroelectric dams in large river basins of South America, like the Parana [142] and Sao Francisco [143; 144]. Despite the existence of specific legislation dealing with non-native and invasive species by the Brazilian Environment Minister (CONABIO 07), there have been no ecological assessments dedicated to them. Some recent studies incorporated probabilistic sampling, threshold analyses and citizen monitoring. Probabilistic study designs have allowed expansion of site results to entire catchments or hydrologic units (e.g., [122; 145; 146]).