Although British by birth, John Walker has devoted most of his decorated six-decade career to the natural landscapes of his chosen home—New England. A classic cobalt blue is the star of his new show at the Alexandre Gallery. Walker’s first New York exhibition in almost a decade presents 21 never-shown pieces, made between 2021 and 2023. An emotional and vibrant love letter to the beauty of Coastal Maine, Walker sees water in graphic, almost abstract terms—streaming, curving, cresting. —Lucy Horowitz