sentences:  Upper Klamath Lake is the largest present-day body of water in the Klamath River watershed, covering on average, with a shoreline of .It is also the largest freshwater lake in the state of Oregon.Historically, Lower Klamath Lake and Tule Lake were one interconnected freshwater marsh that totaled - more than twice the present-day dimensions of Upper Klamath Lake, and larger than Lake Tahoe in central California.