Marshall's lyrical study of a Massachusetts beaver pond parallels a public television film of the same pond. Beginning in January and moving through the year, she follows changes in color and activity level, and embellishes her text with private observations and biological particulars--on beaver (""expert conservationists"") and other species. Winter, a humorless time, presents a landscape without pigment--the occasional deer, cattails, wild turkey. ""March is the pivot month"" when the sun is ""a maker of puddles,"" and spring is the ""grandest chaos""--lemony hues and a long all-you-can-eat dinner. In the waterlily-covered pond in summer, activity decreases around noon--warm water dissolves less oxygen--but dragonflies pass by, their wings like leaded windows. By fall, the trees begin to bald, the pond takes on ""its first thin skin of ice,"" and Marshall comments, for the first time, on the pond's antiquity, her own newcomer status. Such year-long commentaries are almost standardized by now, but Marshall, the author of a praised first novel (Gus in Bronze, 1977), suffuses these exteriors with a personal light--longing to join leaping frogs in their erotic activity, enjoying the frantic acrobatics of water birds as a blimp hovers overhead, extending full appreciation to beaver ingenuity. More than a hundred photographs are promised, which should increase appeal--the samples are auspicious.