page_title: Bronx River
section_title: Ecology
hierarchical_section_title: Bronx River / Ecology
caption_attribution_description: English: The Bronx River
context_page_description: The Bronx River, approximately 24 miles long, flows through southeast New York in the United States and drains an area of 38.4 square miles. It is named after colonial settler Jonas Bronck. The Bronx River is the only fresh water river in New York City.
  It originally rose in what is now the Kensico Reservoir, in Westchester County north of New York City. With the construction of the Kensico Dam in 1885, however, the river was cut off from its natural headwaters and today a small tributary stream serves as its source. The Bronx River flows south past White Plains, then south-southwest through the northern suburbs in New York, passing through Edgemont, Tuckahoe, Eastchester, and Bronxville. It forms the border between the large cities of Yonkers and Mount Vernon, and flows into the northern end of The Bronx, where it divides East Bronx from West Bronx, southward through Bronx Park, New York Botanical Garden, and the Bronx Zoo and continues through neighborhoods of the South Bronx. It empties into the East River, a tidal strait connected to Long Island Sound, between the Soundview and Hunts Point neighborhoods.
context_section_description: Local alewife, taken from a coastal tributary in nearby Connecticut, were released in the river in March 2006. The alewife were expected to spawn in the river's headwaters. Their offspring would spend the summer in the river, migrate out to sea in the fall, and in three to five years return, like all anadromous fishes, to their spawning grounds. Stocking was intended to be repeated annually for the following five years, to build up the new resident population. The fishes, among a group called "river herring," feed low on the food-chain and help reduce eutrophication. And in fact, several adult alewife were found below the first dam on the river on April 7, 2009.  As an analysis revealed they were 3 years old, the assumption of scientists is that these were in fact descendants of the alewife released 3 years before in March 2006. The next step will be to erect fish ladders over the 3 dams lowest on the river, allowing the alewife access to a portion of the river with more suitable spawning habitat.
  In February 2007 biologists with the Wildlife Conservation Society, which operates the Zoo, spotted a beaver (Castor canadensis) in the river. "There has not been a sighting of a beaver lodge or a beaver in New York City for over 200 years. It sounds fantastic, but one of the messages that comes out of this is if you give wildlife a chance it will come back," said John Calvelli, a spokesman for the Society. The beaver is named Jose Serrano, after the Congressman, and was sighted below the East Tremont bridge at Drew Gardens as recently as June, 2009. Beaver had not lived in New  York City since the early 19th century when trappers extirpated them completely from the state. In the summer of 2010 a second beaver joined Jose, doubling the beaver population in New York City. Beaver were once important to the city's economy and pair of beaver appear on the city's official seal and flag.
caption: The river in winter
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