The marine otter (Lontra felina) is a little-known South American otter of conservation concern. We report the 1st detailed information on its activity patterns, home ranges, core areas, and territoriality from 6 otters radiotracked near a fishing village in central Chile. Marine otters were solitary; females exhibited intrasexual territoriality, but there was no territoriality between males or between sexes. Home ranges were ≤4,134 m long and <110 m wide, and range size did not differ between sexes. Marine otters spent 81% of their time on land, mostly resting, with no preference for day or night. Hence, core areas were associated with resting places and dens. Otters concentrated their activity in the littoral zone associated with refuges on land and with fishing waste, which was used as a food resource. Availability of land refuges, combined with their proximity to food resources, could be a decisive factor influencing the distribution of L. felina.