Since 1964, an ice boom has been installed at the mouth of the river at Lake Erie, stretching from Buffalo, New York to Fort Erie, Ontario to prevent the big sheets of ice from floating down the river, going over Niagara Falls, and causing damage. It is 1.7 miles, 2.7 kilometers long. Floating on steel pontoons that are anchored to the river bed, the boom is installed when the water temperature reaches 4 C or on Dec. 16—whichever comes first. It is usually removed on April 1 or when there is less than 645­square­kilometres of ice in the eastern portion of Lake Erie.The ice boom is jointly owned by the New York State Power Authority and Ontario Power Generation.