# The Biological Assessment and Rehabilitation of the World's Rivers: An Overview
## 3 River Rehabilitation
### North America  
To date, the results of the NRSA national and ecoregional assessments in the USA have not led directly to any major stream or river rehabilitation program. However, the 1972 Clean Water Act authorized funds and technical expertise that led to substantial improvements in lactic ecosystem quality across the entire USA, particularly as a result of industrial and municipal waste treatment. Unfortunately, there was no national rigorous ecological monitoring program for assessing the biological results of those efforts. Nonetheless, states with long-term ecological monitoring programs offer pertinent results. For example, Ohio EPA (2016) determined that the percent of river kilometers assessed statewide that met aquatic life standards increased from 20% in 1980 to 75% in 2018. Following basin-wide waste treatment in Oregon's Willamette River, the numbers of fish species and intolerant fish species increased, whereas the number of tolerant fish species decreased in the mainstream river (2018). Most recent rehabilitation projects have been localized, and very few of those have been accompanied by rigorous ecological BACI (before after control impact) monitoring, despite billions of dollars spent on them ([PERSON] et al., 2018). [PERSON] et al. (2018) suggested rehabilitating western USA rangelands and riparian zones simply by excluding livestock and allowing time for the catchments, streams and riparian zones to recover naturally. [PERSON] et al. (2018) recommended that ecological success of rehabilitation projects should be based on (1) what constitutes an ecologically healthy river, (2) improved ecological condition, (3) minimal continued maintenance, (4) minimal harm during the rehabilitation project, and (5) BACI ecological assessments and public reporting. Although [PERSON] et al. (2018) examined 345 stream rehabilitation studies, firm conclusions about the effectiveness of most of them were hindered because of insufficient ecological and historical information, failures to understand catchment processes, and poor monitoring designs. However, reconnecting isolated habitats, rehabilitating floodplains, and improving instream habitat often increased local fish abundance. They recommended protecting high-quality streams and ensuring stream connectivity and watershed processes before attempting instream rehabilitation projects. Similarly, [PERSON] et al. (2018) reported that fish and benthic macroinvertebrate diversity of rehabilitated and unrehabilitated urban stream sites were similar and less than in reference stream sites because of overall catchment conditions. [PERSON] and [PERSON] (2018) concluded that reach-extent mitigations are ineffective for reversing the chemical, physical and hydrological alterations that limit sensitive taxa and water quality improvement. Nonetheless, there are examples of successes, mostly focused on fish assemblages through the addition of instream structures (e.g., large wood and rock; ([PERSON] et al., 2018)) channel reconstruction, naturalized instream flows, fish passage improvements, and restricted livestock grazing ([PERSON] et al., 2018; [PERSON] et al., 2018). Unregulated agriculture and insufficiently regulated urban effluents are the current major threats to attaining good ecological condition in most USA lytic ecosystems ([PERSON] et al., 2018; [PERSON] et al., 2018). Additional threats stem from metal and coal mining ([PERSON] et al., 2018), unregulated oil and gas production ([PERSON] et al., 2018), unregulated livestock grazing ([PERSON] et al., 2018), dams and diversions ([PERSON] et al., 2018), exclusion of headwater streams and wetlands from CWA protections ([PERSON] et al., 2018), and climate change ([PERSON] et al., 2018). However, the drivers of these pressures are continued economic and population growth ([PERSON] et al., 2018), significant declines in state agency staffing and funding ([PERSON] et al., 2018), and direct and indirect weakening of state and federal environmental standards ([PERSON] et al., 2018; [PERSON] et al., 2018).