In 1938, the Bluewater Bridge was built to join Sarnia with Port Huron, Michigan; in 1997, the bridge was twinned. Linking Ontario Highway 402 with the US I-94, the bridge is one of the most important gateways on the north/south truck routes. This bridge to America had been preceded by the construction of the St. Clair tunnel in 1891 - the first rail tunnel ever to pass under a river. The tunnel was an engineering marvel in its day, achieved through the development of original techniques for excavating in a compressed air environment.
When World War II threatened tropical sources of natural latex for rubber, Sarnia was selected as the site to spearhead development of synthetic petroleum-based rubbers for war materials. Large pipelines bring Alberta oil to Sarnia, where oil refining and petrochemical production have become mainstays of the city's economy. Large salt beds found under the city became a source of chlorine and another significant ingredient in the success of the "Chemical Valley."
While industry expanded south along the St. Clair, Sarnia's population tended to move out eastward along the Lake Huron shoreline. The sandy freshwater beaches are a popular tourist attraction, while the sheltered harbor houses marinas for recreational sailing. Since 1925, the 250-mile Mackinac race from Sarnia/Port Huron to Mackinac Island, at the north end of the lake, has been the highlight of the sailing season, drawing more than 3000 sailors each year.
Famous people from Sarnia include:
According to the 2001 Statistics Canada Census:
| North: Lake Huron | |||||
| West: Point Edward |
Sarnia | East: Plympton-Wyoming | |||
| South: Sarnia 45, St. Clair |