Goose Lake is a large, shallow alkaline lake on the Oregon-California border in a basin that is usually closed but, in rare high-water years, can overflow south into the Pit River and the Sacramento River system. A Pleistocene pluvial remnant formed by precipitation and glacial melt, it has fluctuated dramatically and has dried up completely several times. Water diversion lowered the lake below its outlet, shifting the Pit River’s source south of the lake, while rising salinity has put pressure on fish populations. The lake also lay along the Applegate-Lassen Cut-Off, an important emigrant route into California during the Gold Rush era.