The St. Croix River near Stillwater is the region of the river that starts just upstream of where the river widens into Lake Saint Croix and extends down to about where Valley Creek enters the river. The Carnelian-Marine Outlet, Silver Creek, Browns Creek, and Valley Creek all enter this section of the St. Croix River. Additionally, the St. Croix Valley Wastewater Treatment Facility discharges into this section of the reach. This area also marks the farthest extent of the USACE's 9-Foot Channel Navigation Project on the Minnesota River, which ends at river mile 24.5 near downtown Stillwater.St. Croix River at Stillwater, River Mile 23.3 is the main river monitoring station on this stretch of the river. It measures the water quality of the St. Croix River that enters the seven county metropolitan area before it flows past the St. Croix Valley Wastewater Treatment Facility and into Lake St. Croix. On the rare occasion this monitoring station was inaccessible due to construction on the bridge the samples are normally collected from, water samples were collected just upstream at river mile 23.4.The St. Croix River is a 164 mile tributary of the Mississippi River which begins in Douglas County of northwestern Wisconsin. It flows into the Mississippi River near the city of Prescott, WI. The watershed of the river covers approximately 7,760 square miles, split between Minnesota and Wisconsin. It is mostly covered with forests and wetlands, although there is still a sizable amount of agriculture in the south. Development also continues to grow in the St. Croix River watershed. The St. Croix River is designated as a National Scenic Riverway by the federal National Wild and Scenic Rivers Program.