Here the upper Niagara River divides into two channels, with the American Rapids to the left and the Horseshoe Rapids carrying the other 90% to the right. In the distance are Grand Island and Navy Island, the two largest islands in the river. A sandbar once extended east from here, making it possible for people to travel over its shallow waters to Goat Island, but it was removed in the 1950s to prevent the formation of ice jams. The Niagara River is home to many species of waterfowl and gulls and serves as a stopping area for migratory species from around the world. The Niagara River corridor annually supports one of the largest and most diverse concentrations of gulls in the world, and Bonaparte's gull, the herring gull, the canvasback, and the common merganser gather here in globally significant numbers. In 1996, this corridor was designated a globally significant Important Bird Area, becoming the first international site with this recognition. The river-control structure extending into the Horseshoe Rapids, called the International Niagara Control Works, regulates the flow of water over the falls through a series of gates. By international treaty, a controlled flow of water must go over the falls, and the rest is used equally by the United States and Canada for hydroelectric power. The Niagara River also has one of the most diverse populations of fish in North America.