Several engineering schemes are now planned or are in various stages of completion to dam, divert, regulate, or otherwise control the flow of several major waterways in the Canadian sub-Arctic. This region, which contains many large river systems (Map 1), is viewed by a number of federal and provincial government departments as a source of reliable and relatively inexpensive electricity to satisfy the energy-deficient markets of southern Canada and northern United States. However, opposition to these hydroelectric schemes is being voiced across Canada by critics who view them as having or likely to have negative effects on the environment and on the native peoples who inhabit the region. This review examines some of the alleged benefits and costs of four of the most controversial and best publicized of these projects. The information has come from a variety of sources: published literature and press reports, unpublished government documents and consultants' reports, notes taken at public hearings in 1972 and 1973, discussions with government officials, consultants, and other investigators between 1969 and 1974, and research by the senior author between 1968 and 1973 on the effects of hydroelectric developments on the northern environment (Gill, 1971; 1972a, 1972b; 1973a, 1973b, 1973c, 1973d; 1974; Kellerhals and Gill, 1973).