Overview Lake Mary is the star of the Mammoth Lakes region. Of the 11 lakes in the area, Mary is the largest and most developed. Lake Mary Campground is a large facility with plenty of amenities in and around it. The lake provides a great base for activities like fishing, viewing waterfalls, hiking and backpacking.Recreation Lake Mary receives the highest number of trout stocks in the Mammoth Lakes Basin, and is well-known to anglers for its rainbow, brook and brown trout fishing. No swimming o