I examined the characteristics and dynamics of a population of wild steelheadOncorhynchus mykissin the Little Manistee River, an extremely stable-flow, low-gradient (sandy) tributary of Lake Michigan. I monitored autumn pan populations by electrofishing (1981–1983), and I monitored spring emigrant populations at a weir near the river mouth (1982–1984) and both autumn- and spring-returning adults at this weir (1979–1987). Relative to other Great Lakes populations, steelhead in the Little Manistee River had several notable characteristics that are probably linked to abundant groundwater and stable flows: (1) high abundances of age-1 parr, smolts, and adults, (2) constant autumn age-1 parr densities, (3) few emigrant parr, (4) fast growth when in the stream environment, and (5) relatively late age at maturity (after 3 years in the lake). An excessive sand bed load occurs in the low-gradient sections of the river, limiting gravel spawning areas to higher-gradient sections. This limited spawning area likely caused the relatively low abundance of age-0 parr, and may also be a factor in late age at maturity. Abundance and age structure of returning adults varied because of (1) variable survival during the presmolt winter (13–90%), (2) variable survival from smolt to maiden adult (6–29% for spring-run maiden spawners), and (3) variable survival to repeat spawn (3–58%). Most adults returning from a marked smolt cohort originated in the Little Manistee River (mean ± 95% confidence limit, 71 ± 28%). Management of such populations needs to focus on protecting and enhancing the stream environment, and on managing sport harvest. Modeling population dynamics will require development of long-term data sets.