Question: "This is a tough question with a terrible photo, but can you see this bird that we saw today in the Washington Park Arboretum? It dove under and swam away, afraid of us as we got close. It’s in the water on the middle left of the photo….Long slender neck, black and white head…. Thanks!"Tera, near Portland, Oregon
Answer: I took the liberty of cropping your photo to better see the bird. So now the bird is in the lower right portion. The ID features of this water bird are the long dagger-like yellow bill, dark gray back, hind-neck, and crown, with white underparts. The long neck is a distinctive field mark, as you note. The diving behavior is important to note.
Your bird is a Western Grebe. They are rather uncommon winter visitors to deep lakes and rivers west of the Cascades. They winter commonly on the ocean.
Western Grebes breed in the Great Basin and Prairies from central Canada south into California and northern Mexico. In the Pacific NW they breed primarily east of the Cascades, but a few breed at Fern Ridge Reservoir near Eugene, Oregon.
For more information on Western Grebe, please visit the Cornell lab of ornithology's online field Guide.