Mount Bretherton is a 5,960-foot summit in Washington's Olympic Mountains, within Olympic National Park, just south of Upper Lena Lake. Named in 1890 for Bernard Joseph Bretherton, an English-born naturalist who joined Lieutenant Joseph P. O'Neil's east-to-west Olympic Mountains Exploring Expedition, it rises sharply from the surrounding landscape, climbing about 1,400 feet above the lake and more than 5,100 feet above the Hamma Hamma River in two miles. Runoff drains through Boulder, Delta, and Lena Creeks. Shaped by the Olympics' wet marine west coast climate, the mountain is usually best approached in summer, with a non-technical but strenuous route from Upper Lena Lake.