Owyhee (oh -WHY- hee) Reservoir or Owyhee Lake is a reservoir on the Owyhee River in Malheur County, Oregon. Located in far Eastern Oregon near the Idaho border, the reservoir is Oregon's longest at 52 miles (84 km). The name of the lake is from the older spelling of "Hawaii." It was named for three Hawaiian trappers, in the employ of the North West Company, who were sent to explore the uncharted river. They failed to return to the rendezvous near the Boise River and were never seen again. Due to this, the lake and its region were named "Owyhee.