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compared to equivalent features in large-scale hydro plants. The principal impacts of small-scale hydroelectric facilities affect fish population through effects on migration, reproduction, and rearing and resident adult habitat. Birds and terrestrial animals also may be impacted from certain facilities, such as transmission towers and canals. Hydroturbines suitable for small-scale use include the conventional impulse and reaction types, including Pelton, Cross-flow, Francis, and pro- peller designs. Recently, several unconventional turbine designs have been proposed especially for use in small-scale plants. Turbines of all types can injure and kill fish; the extent of the effect varies according to fish species and size, turbine design, turbine operating efficiency, and other factors. Predicting turbine impacts on fish is difficult because many of the possible combinations of turbines and fish have never been tested and because existing. test results are inconclusive. Most of the unconventional turbine designs have never been tested in terms of resulting fish mortality, and their design often is sufficiently different from that of older turbines to make impact prediction based on existing data highly unreliable. Small-scale hydroelectric projects operate in run-of-river, peaking, or seasonal store and release modes. The main concerns associated with these operational modes are alterations of the physical, chemical and biological features of habitat which can affect all life stages of fish and other species of concern. Instream flow alterations may lead to fish stranding and a reduction in the transport of nutrients, plankton, and sed- iments essential for the maintenance of downstream biological productivity. Adverse impacts may also result from routine maintenance of small-scale hydro facilities which typically involves cleaning and disposal of debris, trimming of site vegetation, and equipment overhaul. Required maintenance that necessitates extensive site work may result from floods, sediment accumulation, or structural defects and may have serious impacts if not accomplished with care. More than 100 possible types of environmental associated with small-scale hydroelectric technology. wi 11 have a 11 of these impacts, however. Major impacts small-scale hydro sites in the United States include: 1. Blockage (and mortality) of both upstream- and downstream- migrating fish by dams, diversion structures, turbines, spillways, and waterways; impacts have been Not all projects that are common to 2. Alteration of stream and riverine habitats, natural lakes, riparian areas and wetlands by inundation, dewatering, channelization, and filling; 3. Changes in water quality, including changes in sediment transport, dissolved oxygen, and water temperature; v