St. Marys River, Michigan–Ontario – WorldAtlas

The St. Marys River is a 119.9 km long river that begins at the end of Whitefish Bay and connects Lake Superior and Lake Huron. The river forms part of the border between Michigan, USA, and Ontario, Canada. The 4.5 km long Sault Ste. Marie International Bridge spans the St. Marys River, connecting the twin communities of Sault Ste. Marie of Michigan and Sault Ste. Marie of Ontario. Both Canada and Michigan have strong tourism economies based on recreational activities such as sport fishing on the St. Marys River.

Geography of St Marys River

Aerial drone view of the St. Marys River
Drone view of the St. Marys River between Lake Superior and Lake Huron with water channels running through landscapes between Canada and the USA.

The headwaters of the St. Marys River has a drop of 7.0 m and begins at the end of Whitefish Bay on the eastern tip of Lake Superior before flowing 119.9 km southeast into Lake Huron. The distance between the lakes decreases by 22 feet on average. At Brush Point, the narrowest point above the rapids, the width ranges from 25,000 feet at the mouth of the river to about 2,000 feet. Close to Sault Ste. Marie City, Ontario, the river falls more than 20 feet for 1 mile (1.6 km) through the St. Marys Rapids. The lower river flows about 45 miles from the base of the St. Marys Rapids to Point Detour on Lake Huron.

The river splits into two channels about two and a half miles below the rapids, with one channel running through the north end and the other going west of Sugar Island. The Northern Channel flow continues through Lake George before joining the North Channel of Lake Huron just north of St. Joseph Island. The river discharges an average of 2,135 cubic meters of water per second. American tributaries of the St. Marys River include the Charlotte River, Gogomain River, Little Munuscong River, Munuscong River, and Waiska River. The river’s Canadian tributaries include the Big Carp River, Bar River, Desbarats River, Fort Creek, Garden River, Two Three River, Lower Echo River, Little Carp River, and Root River. There are a few islands in the St. Marys River including Lime Island, Whitefish Island, Sugar Island and Neebish Island.

Climate of St. Marys River

St. Mary's River in the middle of winter.
St. Mary’s River in the middle of winter. Image credit: United States Coast Guard, CWO Dale Hoornstra, public domain, via Wikimedia Commons

There are three distinct stages of ice conditions in the St. Marys River. Mid-December to mid-January marks the beginning of the autumn frost phase. This period lasts until the main part of the river is completely covered with solid ice. To prevent more ice from entering the rapids, an ice bridge can be built over the equalizers.

Deep winter lasts from mid-January to mid-March, and for most of that time upper and lower river ice conditions are fairly stable. Typically, the spring break season lasts from mid-March to mid-April. Warmer temperatures and westerly winds allow large amounts of ice to flow through the equalization works and rapids.

Brief History of the St. Marys River

The Soo Locks in Sault Ste Marie, Michigan.
The Soo Locks in Sault Ste Marie, Michigan.

The St. Marys River served as an important part of the fur trade route after Étienne Brule’s exploration of the area in 1621. Fort St Joseph was built in 1796 in part to control trade on this congested route and to ensure its important strategic location. The region remained under British control throughout the War of 1812. The state of Michigan built America’s first shipping canal in 1855 in the St. Marys River on the south side of the rapids. The canal was expanded by the United States government in 1871 and was granted federal status in 1881.

The US Shipping Canal was still being improved until September 1919 when four locks were in operation. The Canadian Navigation Channel lock on the north side of the rapids was operational in September 1895. In 1959 the Soo locks were incorporated into the Great Lakes Waterway network. The combined American-Canadian “Soo Locks” was for many years the busiest such system in the world. Parks Canada, whose mission is to protect and interpret the canal’s natural and cultural values, assumed management of the Sault Ste. Marie Canal in 1985. When the lock wall failed in 1987, a recreational lock was added to the original design and the canal was ceremoniously reopened on 14 July 1998.

Power plants in St Marys River

The 116-year-old Edison Sault Hydroelectric Power Plant in Sault Ste.  Marie, Michigan
The 116-year-old Edison Sault Hydroelectric Power Plant in Sault Ste. Marie, Michigan. Editorial Credit: PQK /

Saint Marys Falls Hydroelectric Power Plant, also known as Edison Sault Hydroelectric Plant and Cloverland Electric Cooperative Hydroelectric Plant, is located near Sault Ste. Marie, Michigan, just east of the Soo Locks. This engineering marvel has been powering the people of the Upper Peninsula for over a century. At 1,340 feet long and 80 feet wide, it is one of the longest hydroelectric dams in the world. The plant includes 74 three-phase generators with a total output of 25 to 30 megawatts. It has intricate stonework and was built of steel and red sandstone.

Ecology of the St. Marys River

The area along the St. Marys River is home to several different natural tree species, such as willow, river birch, and a number of oaks. Whitetail deer, black bear, bobcat, river otter, beaver, raccoon, alligator, gopher tortoise, red woodpecker and wild turkey. The river also offers fantastic fishing for bass, walleye, whitefish, salmon, pike, smallmouth bass and a species not well known outside of northern Michigan: the sea herring or cisco.

Threats to the St. Marys River

The US and Canadian governments identified 43 sites in the Great Lakes region that had serious and ongoing environmental problems in the 1980s. These areas are referred to as Areas of Concern (or AOCs). One of Michigan’s twelve remaining AOCs is the St. Marys River, which is also one of two sites shared internationally with Ontario, Canada. The Canada-US Great Lakes Water Quality Agreement designated the St. Marys River as a Binational Concern (AOC) in 1987. The deteriorating water quality and environmental health of the watercourse has been caused by industrial and sewage pollution, as well as changes in the watercourse.

Approximately 70 miles from the mouth of the river at Whitefish Bay between Point Iroquois and downstream to De Tour Passage constitutes the affected region. Pollutants from point discharges from industry and cities on both sides of the St. Marys River have adversely affected water quality, sediments and biota. The sediment has been contaminated by industrial and municipal discharges (PAH) with various pollutants, suspended matter, metals and polycyclic aromatic hydrocarbons. In addition to industrial and municipal discharges, pollutants in the AOC also come from tanneries, a steel mill, discharges from wastewater treatment, mixed water overflows and various non-point sources.


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