Tatla Lake is situated on the western edge of the Chilcotin Plateau, and some of the largest mountains in British Columbia are found to the west including Mount Waddington - the tallest mountain completely within British Columbia's border. The Coast Mountains block most of the moisture traveling off the Pacific Ocean leaving the entire Chilcotin region in a rain shadow. Tatla Lake is the westernmost location for many semi-arid plants like Prickly Pear Cactus and Rabbit Brush.