economy dominating in the north and west; in the 19th century, agriculture and lumbering were important east to the St. Clair River. Sugar beets were cultivated and annual festivals were held at harvest time. In addition, many farms had mixed agriculture. There are steep hills and small canyons near the Black River. Since the mid-20th century, manufacturing had dominated in and around Port Huron. Tuscola Like Huron County, Tuscola is mostly dependent on agriculture. Industries such as sugar refining and ethanol processing, as well as growing various grains and beans, make up most of the economy. Caro, one of the largest cities in The Thumb (the largest if you exclude St. Clair and Lapeer Counties), is named after Cairo, Egypt and is the county seat. Tuscola County only has of shoreline along Saginaw Bay, so it is not as dependent on tourism as the other counties in the area. Tuscola County is economically tied to the surrounding region as well as to the Saginaw, Bay City, and Flint areas. Borderline regions The boundaries of what is included in the Thumb are often debated, but nearly all definitions include Huron, Sanilac, and Tuscola counties, known as the tri-county region. Disputed areas include: St. Clair County, especially the southern portion, as the county is now classified as part of Metro Detroit by the Census Bureau. Lapeer County Richmond and northern Macomb County. Genesee County Blue Water Area The Blue Water Area is another term describing the Thumb of Michigan. The term usually applies to St. Clair County and surrounding areas. The title is also extended to include all of Michigan's Thumb. The name refers to the county being bordered by water: on the east is the St. Clair River, connecting Lake Huron to the north to Lake St. Clair. Below that is the Detroit River. The namesake Blue Water Bridge spans the St. Clair river, connecting Port Huron to Sarnia, Ontario. A similar name, "Blue Water Country," is used to describe the same region on the Canadian side. Discover the Blue Discover the Blue is a promotion by the Blue Water Area Convention and Visitor's Bureau. It is designed to attract visitors to the shoreline of eastern Michigan. Communities participating in Discover the Blue include Algonac in St. Clair County (at the southern end of the Thumb) and others to the north, such as Port Austin (at the tip of the Thumb).