It was sitting in shallow water right in front of me, ignoring me. So I took its photo. It is starting to get its gray feathers on its back yet still has a lot of brown on the wing tips and tail along with brown speckles. The bill and legs are still pink, rather than the adult yellow. The eyes are dark whereas an adult would be yellow. The black covers the end of the bill rather than forming a ring. All of which age it as a first winter bird. Ring-bill gulls take 3 years to mature into adult plumage.
First Winter Ring-billed Gull (Larus delawarensis)