Unique Features: The Cassimer Bar great blue heron and double-crested cormorant rookery is located at the confluence of the Okanogan and Columbia rivers. The rookery is a large collection of giant nests high up in the branches of a white poplar (populous alba) tree grove. Herons and cormorants typically nest communally in what are called “rookeries”. However, it is relatively unusual to see these two species nesting together. The rookery can best be viewed from the highway or from a boat. When standing beneath the rookery during nesting season, various squawking, grunting, clucking and other sounds can be heard, much like one might hear in a jungle. Nesting season here is May through July.