Located between the Peace and International Bridges is Squaw Island. Extending upstream of this island is Bird Island Pier, which proceeds south under the Peace Bridge and out into Lake Erie. The channel east of Squaw Island and the Bird Island Pier is known as the Black Rock Canal. At the north end of this channel, just downstream of the International Bridge, is the Black Rock Lock. The Black Rock Canal and Lock allow for passage of commercial vessels around the shallow and fast moving waters at the head of the river. The depth in this canal is 21 feet. In the first 4 miles of its course the river falls about 5 feet. The level in the canal is maintained near the level of Lake Erie and the lock raises and lowers ships over the 5-foot difference.

In the next 18 miles, the river flows more slowly, falls only about 4 feet and widens to 2,400 feet. Within this 18 mile reach, about three miles downstream of the Black Rock Lock, the river divides into two channels around Grand Island, the Chippawa Channel to the west of the island and the Tonawanda Channel to the east. Both channels are navigable. The Chippawa Channel has minimum depths of 10 feet below Chart Datum. The Tonawanda Channel has been improved to a depth of 21 feet to Niagara Falls, New York.

Downstream of Grand Island, the river rejoins to form the Chippawa-Grass Island Pool. At this point, the river is shallow and about 7,000 feet in width; however, the steep slope and rapid current in the area make the term "pool" a misnomer. Both the United States and Canada divert water out of the river from this pool for power generation. To maintain optimum water levels in the pool for power production, a control structure was built just above the first of the cascades above the falls. This gated structure extends half way across the river.

In the mile below the Chippawa-Grass Island Pool, the river falls 55 feet, as cascades and rapids above Niagara Falls. The river divides into two channels around Goat Island before it plunges over the Niagara Escarpment into the Maid-of-the-Mist Pool, 162 feet below. The larger channel, on the Canadian side, ends as the Horseshoe Falls. The smaller channel, along the U.S. side, is subdivided by a number of islands. One of the principle islands, Luna Island, is located on the crest of the American Falls and separates a smaller cataract, the Bridal Veil Falls, from the main cataract.

The Horseshoe Falls is at the head of a narrow gorge that has been formed by the recession of the Falls. The upper layers of rock at the crest of the Niagara Escarpment are of limestone, hard and resistant; whereas, the lower layers are chiefly shales and sandstones, comparatively weak and easily eroded. As the softer rock is worn away below, the hard upper beds are undermined and from time to time sections break away and the crest is modified. In the center portion of the Horseshoe, the rate of recession was 4.2 feet per year from 1842 to 1905-06 and 3.2 feet per year from 1905-06 to 1927. It was noted that a maximum recession of 50 feet occurred from 1927 to 1950, which is at the rate of 2.2 feet per year. These figures indicate that the rate has been less since 1906 than it was during the preceding 60 plus years. It was theorized that the tendency would be for the rate of recession to decrease in the future, mainly due to the fact that the limestone strata are thicker upstream and because the rivers two main channels, which once actually joined near the toe of the Horseshoe, are being separated more and more as the Falls recede. Also, it was noted that the rate of recession varies with the volume of water flowing over the Falls; that is, the greater the volume, more the recession. Since the American and the Horseshoe Falls separated, as the latter receded upstream, recession at the American Falls has been very slow. It was stated that the flow is distributed along the crest of the Falls in a manor such that the discharge per foot for the American Falls, relative to that for the Horseshoe Falls, is small.

In the first 6 miles below the falls, the river falls 96 feet, as it travels through the narrow gorge. Directly below the falls, the river flows in the deep channel of the Maid-of-the-Mist Pool for about 2 miles before entering a narrow, shallow channel known as the Whirlpool Rapids. The Maid-of-the-Mist Pool is relatively flat with a total drop of only 1.4 feet and is navigable throughout most of its length.

The Whirlpool Rapids, a wild, precipitous reach of the river, which in a little more then a mile drops about 50 feet, terminates in the Whirlpool, a mile downstream of the Maid-of-the-Mist Pool. The Whirlpool is a circular basin in which the direction of the river is turned nearly ninety degrees. The river continues another 4 miles through the Lower Rapids, at practically undiminished speed. As the river leaves the gorge, at Queenston, Ontario, it widens out. It is at Queenston-Lewiston that the power companies return water to the river. The remaining 4 feet of fall to Lake Ontario produces only a moderate current in the final run of 7 miles.

One of the earliest projects to be attempted on the Niagara River was the construction of a pier from Bird Island to Squaw Island, begun in 1823 and completed in 1825. As part of this project, a dam and a timber ship lock were constructed at the lower end of Squaw Island between the island and the U.S. mainland. In 1851, the timber lock was replaced by a stone lock. The pier was extended upstream 900 feet in 1891 and to about 3,100 feet in 1901. Improvements in the Black Rock Lock and Canal and the Bird Island Pier also occurred in 1930-31 and 1944-45. The later additions to the Bird Island Pier reduced the width of the river, particularly at the point where the channel crosses under the Peace Bridge.

The first major change affecting the total flow of the Niagara River was the construction, in 1872, of the International Railway Bridge. The piers of this bridge restricted the cross-sectional area and reduced the flow for the same Erie stage. The next change in the channel cross-section was due to the construction of a water intake structure by the City of Buffalo, New York in the 1880s. This structure was placed about 1-1/2 miles upstream of the International Bridge, near midstream.

During the 1880s and 1890s, several dredging projects took place in the upper river; primarily between the head of the river and Tonawanda Harbor, to improve navigation. Between 1905 and 1925, 12,867,000 cubic yards of material were removed from the Niagara River. Of this amount, approximately 8 percent was removed by the United States for the benefit of navigation. Much of the remainder was taken out near the head of Grand Island by commercial interests. Little is known regarding the time of removal by commercial interests. However, it has been estimated that in 1924 and 1925 alone over 2,000,000 cubic yards of material were removed. This dredging was in shallow water, and an attempt seemed to have been made to leave a shallow area immediately above the work. All permits for dredging sand and gravel from the United States portion of the river were cancelled in May 1926.

Beginning in 1918, water was diverted from the Niagara River through the New York State Barge Canal, mainly for navigation purposes. This water, between 700 and 1,000 cfs, is diverted from the river at Tonawanda, New York and returned to Lake Ontario via the Oswego and Genesee Rivers and the Oak Orchard and Eighteen Mile Creeks, in New York State. Also in 1918, the approach channel leading to the intakes of the Niagara Falls Power Company was deepened and 200,000 cubic yards of rock were dumped in the Chippawa-Grass Island Pool. In addition, from 1919 to 1921, while the intake for the Queenston Power Plant was under construction, large quantities of earth and rock were dumped in the pool below the intake.

In 1925-26, the Peace Bridge was constructed across the narrowest part of the head of the river. This bridge had a considerable retarding impact on the river flow by reducing the already constricted controlling point of flow from Lake Erie.

In the 1930s and 1940s, construction of Mather Park at Fort Erie, Ontario, took place along the shore of the Niagara River in the vicinity of the Peace Bridge and upstream thereof. The park construction involved placement of fill material in the Niagara River and the building of a seawall. This construction had a limited effect on the flow in the river, because the fill was placed in fairly shallow water in an area which often was above water.

The placement of fills downstream of Mather Park for the Nicholls Marine and its adjacent areas at Fort Erie, Ontario, took place at various times until the early 1970s. These fills are located in the river at its narrowest point and have a relatively significant impact on Lake Erie levels, compared to other fills in the area. Fills below the International Bridge on the Canadian shore have also affected the flow in the river, but to a much lesser extent than fills closer to the head of the river.

The first recorded use of the Niagara River for power purposes was in 1725, with the utilization of the rapids above the Falls. The first attempt to develop power from the actual Falls was made in 1853. The first production of electrical power dates from 1877. Since then, there has been a continuous growth, which is now limited only by the control imposed by the Niagara Treaty of 1950. This Treaty, between the Governments of Canada and the United States, requires a minimum flow over the falls of 100,000 cfs between the hours of 8:00 a.m. and 10:00 p.m., E.S.T., from April 1 through September 15, and between the hours of 8:00 a.m. and 8:00 p.m. from September 16 through October 31 (tourist hours). A minimum flow of 50,000 cfs is required at all other times (non-tourist hours).

In 1853, the Niagara Falls Hydraulic Company was incorporated and construction commenced on a canal 70 feet wide, 10 feet deep and 3/4 mile long. Starting at a point about 1 mile above the Falls, on the U.S. side, this canal terminated in a basin about 1/2 mile long located at the edge of the gorge below the Falls. Water was drawn into the canal in 1855 and the canal was considered complete in 1861. It was anticipated that mills would be situated on the edge of the cliff drawing water from the basin and spilling the used water over the cliff. The Civil War brought the project to a stand still and only one mill was established.

In 1877, the above property was bought by the Niagara Falls Hydraulic Power and Manufacturing Company (later known as the Hydraulic Power Company). By 1880, two additional mills were using water from the Niagara River for mechanical power. In 1881, the company installed electric generators and sold electric power to various manufacturers and to the village of Niagara Falls, New York.

In 1886, a competing company was organized, the Niagara Falls Power Company. This company cut a tunnel through solid rock under the City of Niagara Falls; the tunnel, above the Falls, leading to a vertical shaft. Water passed through the tunnel, dropped into the shaft, through wheels at the bottom of the shaft and through a long tunnel with an outlet below the Falls. Power was first delivered from the constructed station, Edward Dean Adams Station, in 1895. The Adams Station is no longer standing.

Prompted by the example of the Niagara Falls Power Company, in 1892 the Hydraulic Power Company enlarged its canal and constructed a second power plant; completed in 1901. In 1904, a new and larger plant was begun; it was finished in 1914. The old tenants of the company were gradually induced to surrender their old water power rights and accept supplies of electric power. The various U.S. power companies on the Niagara River came together in 1918 to form the Niagara Falls Power Company, in order to improve the use of water and increase efficiency to meet increasing demands for electricity. In 1956, the southern two-thirds of the Companys Schoellkopf Plant was destroyed by a rockfall.

The first diversion of water from the Niagara River, by Canada, for power production was in 1893, when a small generating plant was built which diverted water from just above the Falls and discharged it through an outlet in the cliff at the flank of the Horseshoe Falls. The operating head was 62 feet. At the beginning of the 20th century, three large hydroelectric power houses were begun, the Ontario Power Company (1901), the Canadian Niagara Power Company (1902) and the Electrical Development Company (1903), today known as the Toronto Power Plant. This plant was retired in about 1975. In 1900, diversions from the Niagara River, above the Falls, for power purposes, totaled about 6,000 cfs; by 1922, the total amount diverted, by both the U.S. and Canadian plants, was approximately 50,000 cfs.

The first of the high-head plants, the Canadian Queenston Plant (later renamed the Sir Adam Beck No. 1) was completed in 1926, and a further 14,000 cfs bypassed the Falls. During the Second World War, an increase of this diversion, by Canada, was permitted. In 1954, units of the Sir Adam Beck No. 2 Plant came into service. This plant reached full capacity in 1958, bringing the maximum diversion through the Beck development to 66,000 cfs. Both plants divert water from the Chippawa-Grass Island Pool and return it to the Niagara River about a mile upstream of the village of Queenston, Ontario.

The Robert Moses Niagara Plant, on the United States side of the river, came into service in January 1961 and reached full capacity in 1962. It has a design capacity of 83,000 cfs, but on occasion has diverted up to 105,000 cfs. This plant also diverts water from the Chippawa-Grass Island Pool, and returns it to the river about two miles upstream of Lewiston, New York.

In about 1900, in order to facilitate the flow of water into their intake canals and to reduce trouble caused by ice, the Niagara Falls Power Company (U.S.) cut a channel across a shoal area above their intake. This lowered the elevation of the Chippawa Pool. In constructing their intake works in 1903-05, the Ontario Power Co. closed off a portion of the First Cascade with coffer dams. This raised the level of the water above, but the change was temporary. Removal of the dams, in 1905, permitted the water to fall to its original level. In 1918, coincident with the construction of a new intake tunnel, the Niagara Falls Power Company deepened the cut across the shoal and, as previously mentioned, dumped some 200,000 yards of rock into the Chippawa-Grass Island Pool. At about the same time, construction of the Queenston canal began. Much of the dredge material from this construction, mostly earth, was also dumped into the Pool. These dumpings somewhat compensated for the effects of the increased diversions by power, but this material was gradually eroded away.

In 1929, a Special International Niagara Board recommended construction of a submerged weir at the lower end of the Chippawa-Grass Island Pool, to facilitate the diversion of water for power generation, without lowering the level of Lake Erie. Before 1941, the total allowable diversion of water from the Niagara River for power purposes was 56,000 cfs. During 1941, this limit was increased to 82,500 cfs. This increase in diversion highlighted the need for such a weir. Construction of this weir took place between 1942 and 1947. The weir raised the level of the Chippawa-Grass Island Pool, which had been lowered by the power diversions, and improved the flow over the American Falls and in the vicinity of the Three Sisters Islands. However, the weir caused a small decrease in the flow over the Horseshore Falls, thus making the conditions at the flanks of the Horseshoe somewhat less satisfactory.

In 1953, work began on remedial works to replace the submerged weir. The Chippawa-Grass Island Pool Control Structure was completed in 1957, with additions made in 1961-1963. The structure, consisting of 18 movable gates, extends 2,200 feet out from the Canadian shore about a half mile upstream of the Horseshoe Falls. This structure serves to maintain pre-project levels in the Chippawa-Grass Island Pool, so as to provide proper flows over the Falls, while allowing for diversion for power purposes

Niagara Falls history is rich in heritage and interesting facts, from daredevils who have attempted to take on the mighty Falls to electrifying inventors such as Nikola Tesla, best known for his contributions to the design of the modern alternating current electricity supply system. Niagara Falls was formed starting more than 12,000 years ago at the end of the Ice Age when large torrents of water were released from the melting ice, draining into the Niagara River. The water plunged over the edge of the Niagara Escarpment – to what is now known as Lewiston, NY. Eventually, the force of the water wore away the rock layers and Niagara Falls moved upstream, reaching its present location. Year after year, the formation continues with the annual freezing and thawing of the Niagara River, along with gradual erosion and periodic rock-falls. Remedial work has been completed to preserve the Falls and the volume of water has been reduced by diversion for hydroelectric power. Native Americans living in the region were most likely the first people to behold the power of Niagara Falls. After that, Niagara Falls was discovered by French explorer, Father Louis Hennepin in December 1678. The region soon became a French stronghold, as forts were built at the mouth of the Niagara River, controlling access to the Great Lakes. The fort was restored between 1926 and 1934 and is now present day, Old Fort Niagara – an 18th century fortress offering daily programming including live reenactments and demonstrations year-round. Not only are the Falls themselves powerful, but the City of Niagara was the birthplace of hydroelectric power! In 1896, Nikola Tesla developed the alternating current system, which allowed for the transmission of power generated along the Niagara River to homes and businesses. The Niagara Gorge Discovery Center is located above the site of the Schoellkopf Power Station, from which electricity was first sold as a commodity. Today, power plants on both the American and Canadian side of the Falls produce nearly 2.5 million kilowatts of electricity. Power up and explore more at NYPA – Niagara Power Vista where scientific exploration awaits with hands-on interactive technologies, a multi-sensory 4D theatre and more.