A diversity of aquatic and terrestrial organisms populate the Wine Country and its riparian zones. Winter-run Chinook salmon ("Oncorhynchus tsawytscha"), Delta smelt ("Hypomesus transpacificus") and steelhead ("Oncorhynchus mykiss") are the most prominent fishes. Researchers have studied anadromous fish-movements extensively in Sonoma Creek and in the Napa River as well as in the Laguna de Santa Rosa - not only in the mainstems, but in many of the tributaries. These investigations have demonstrated a historical decline in spawning and habitat value for these species, primarily due to sedimentation and secondarily to removal of riparian vegetation since the 19th century.