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. —L.H.