The Neotropical region is here defined as Central America, the Caribbean, and South America. Although parts of South America are not tropical, we include the entire region in the definition. The delineation of the Neotropical region followed the boundaries of the Freshwater Ecoregions of the World (FEOW) classification (Abell et al., 2008; Fig. 12.1). In terms of freshwater resources, 11 major habitat types (MHT) are found within the Neotropical region, including lakes, wetlands, rivers, and floodplains. The 11 MHTs contain a total of 78 freshwater ecoregions (FER), as seen in Table 12.1 (Fig. 12.2A–F). These freshwater ecoregions include true tropical systems, as well as temperate freshwater systems with different areas, climates, and seasonalities. Basically, these ecoregions are in tropical, coastal, montane, temperate, and island climates.