Information on marine mammals and marine birds in US Pacific Northwest waters is limited but necessary to assess potential impacts from proposed and planned human activity (for example, cable installation, energy and port development) as required by regulatory permitting processes, particularly relative to recent plans for offshore wind development. We conducted daily opportunistic, non-systematic observations of marine mammals and marine birds in autumn 2014 and of marine mammals in summer 2015 to meet mitigation and monitoring requirements associated with a geophysical site characterization survey for a proposed offshore wind floating platform demonstration project off Coos Bay, Oregon. Two biologists completed observations during daylight with the naked eye and reticle binoculars from a 17-m vessel between Coos Bay and the proposed platform site 30 km offshore. In 2014, 1058 h (3244 km) of observation occurred during 3 October through 4 November, with 1182 h (4367 km) observations conducted from 10 July through 28 August 2015. In total, 543 groups (approximately 1389 individuals) representing at least 14 marine mammal species and 7444 groups (approximately 18322 individuals) representing at least 22 marine bird species were observed. Sighting rates (number of individuals observed per 100 km of observation) were higher for nearly every species of marine mammal in summer 2015 than autumn 2014. An extralimital sighting of 25 Bottlenose Dolphins (Tursiops truncatus) and 5 sightings of rare transient Killer Whales (Orcinus orca) were documented. Results address a gap in site-specific marine mammal and marine bird baseline occurrence data and information required to assess effects of proposed offshore wind development and other human-related activities near Coos Bay, Oregon, as well as climate and oceanographic changes.