The river is about 56 kilometres (35 miles) long and includes Niagara Falls along its course. The falls are thought to have moved upstream 11 kilometers (7 miles) in the last 12,000 years but modern diversion of the river for power generation has reduced the erosion to a minuscule amount. Power plants on the river are the Sir Adam Beck Generating Station, built in 1954 on the Canadian side, and the Robert Moses Niagara Power Plant, built in 1961 on the American side. The sites generate 4.4 gigawatts of electricity combined. The river flow is also regulated by the International Control Works built in 1954. Shipping on the Great Lakes bypasses the Niagara River and Falls using the Welland Canal, part of the Saint Lawrence Seaway, located on the Canadian side.
The total drop in elevation along the river is 99 meters (326 feet). The Upper Niagara Rapids drop 15 m in the 800 m before the Falls. The Niagara Gorge extends 11.26 km (7 mi.) downstream from the Falls and includes the Niagara Whirlpool and another section of rapids.
The Niagara River features two large islands, Grand Island and Goat Island, both in the United States. The western end of the Erie Canal is near Grand Island. Goat Island and the tiny Luna Island split Niagara Falls into its three sections, the Horseshoe, Bridal Veil, and American Falls. Navy Island, on the Canadian side, is near the north end of Grand Island, and Strawberry Island lies southeast of Grand Island.
The Niagara River and its tributaries, Tonawanda Creek and the Welland River, formed part of the last section of the Erie Canal and Welland Canal. After leaving Lockport, New York, the Erie Canal proceeds southwest until it enters Tonawanda Creek. After entering the Niagara River, watercraft then proceed southward to the final lock, where a short section of the canal allows boats to avoid the turbulent shoal water at the river intake and enter Lake Erie. The first, second and third Welland Canals used the Welland River as a connection back to the Niagara River south of the falls, allowing water traffic to safely re-enter the Niagara River and proceed to Lake Erie.
The Niagara River is crossed by 4 international road bridges:
- The Peace Bridge connects Interstate highway I-190 at Buffalo, New York, and the QEW at Fort Erie, Ontario.
- The Rainbow Bridge is the main road bridge connecting Niagara Falls, New York, and Niagara Falls, Ontario.
- The Whirlpool Rapids Bridge, or Whirlpool Bridge, also connects the two cities of Niagara Falls.
- The Lewiston-Queenston Bridge connects I-190 at Lewiston, New York, and Highway 405 at Queenston, Ontario.
The Whirlpool Bridge also carries railway traffic on a separate deck. There are two other railway bridges adjacent to the Whirlpool and Peace Bridges, respectively.
Two bridges over the east branch of the river, forming part of I-190 on the American side provide a through road link across Grand Island, New York between Niagara Falls, New York, and Buffalo, New York, while the smaller American Rapids Bridge links Goat Island to the American shore.
Cities on the Niagara River include:
- Buffalo, New York
- Fort Erie, Ontario
- Lewiston, New York
- Niagara Falls, New York
- Niagara Falls, Ontario
- Niagara-on-the-Lake, Ontario
- North Tonawanda, New York
- Queenston, Ontario
Several battles occurred along the Niagara River which was historically defended by Fort George (Canadian side) and Fort Niagara (American side) at the mouth of the river and Fort Erie (Canadian side) at the head of the river. These forts were important in the French and Indian War and the American Revolutionary War. The Battle of Queenston Heights took place near the river in the War of 1812.
On the Canadian side of the river the Niagara Parks Commission maintains all of the shoreline property, except the sites of Fort George and Fort Erie, as a public greenspace and environmantal heritage.