Lake Pend Oreille was glacially formed during the ice age. It is also believed that the eastern side of the lake was in the path of the ancient Missoula Flood. The lake sits at the south end of the Purcell Trench, carved by glaciers moving south from Canada. The eastern side of the glacier is believed to have formed the dam for the Missoula flood, at the point where the Clark Fork river enters the lake between the Cabinet and Bitteroot mountains.

The area around the Lake is the traditional home of the Kalispell Indian peoples. A French fur trapper who entered the region in the 1800s is believed to have given the lake its name. The words "Pend Oreille" are French for an ear-hanging or pendant. Ear pendants were characteristic of the Kalispell tribe. The lake is shaped much like a human ear when viewed from above or on a map.

During World War II, the south end was the second largest naval training ground in the world. Built as a result of the Japanese attack on Pearl Harbor, the training station is now Farragut State Park. The lake is still used by the Navy's Acoustic Research Detachment to test large-scale submarine prototypes: the significant depth gives acoustic properties similar to the open ocean. Lake Pend Oreille is a lake in the northern Idaho Panhandle, with a surface area of 148 square miles. It is 65 miles (105 km) long, and 1,150 feet (350 m) deep in some regions, making it the fifth deepest in the United States. It is fed by the Clark Fork River and the Pack River, and drains via the Pend Oreille River. It is surrounded by national forests and a few small towns, with the largest population on the lake at Sandpoint. All but the southern tip of the lake is in Bonner County. The southern tip is in Kootenai County and is home to Farragut State Park, formerly the "Farragut Naval Training Station" during World War II.

The lake is home to many species of fish, including rainbow trout, lake trout, perch, crappie, bass, whitefish and Kokanee. The forests consist of Ponderosa Pine, Douglas Fir, Poplar, Quaking Aspen, Paper Birch and Western Larch. Local animal species include whitetail deer, elk, gray wolves, moose, squirrels, black bears, grizzly bears, coyotes and bobcats, along with bald eagles, osprey, owls, hummingbirds, hawks, woodpeckers, ducks and the mountain bluebird. The lake is a home for several species of migratory water fowl.