I am pretty sure that this is a female hooded merganser, though immature and non-breeding males can look similar. The reason? This merganser was paired with a male with white hood displayed at Delta Ponds.

Regarding identity, 'All About Birds' https://www.allaboutbirds.org/guide/Hooded_Merganser/id), says this about the hooded merganser: "Color Pattern -
Adult male Hooded Mergansers are black above, with a white breast and rich chestnut flanks. The black head has a large white patch that varies in size when the crest is raised or lowered, but is always prominent. Females and immatures are gray and brown, with warm tawny-cinnamon tones on the head."