Most popular accounts hold that the name "Buffalo" is a corruption of the French phrase beau fleuve, "beautiful river," a phrase said to have been exclaimed by French explorers upon seeing the Niagara River. This speculation, however, is contradicted by primary sources. French explorers actually referred to the Niagara River in print as Rivière aux Chevaux, "River of Horses."[20] The earliest name origin theory to appear in print (1825) relates a story about stolen horsemeat being passed off as bison flesh, with the site of the illicit picnic henceforth remembered as "Buffalo," but the author who conveyed this tale expressed his skepticism.[21] What is clear is that there were no bison in the area; that the settlement of Buffalo took its name from Buffalo Creek;[22] and that Buffalo Creek first appeared on a map in 1759–1760.[23] Although the Beau Fleuve theory is the most appealing but least plausible theory among many, it is unlikely that Buffalo's true name origin can be conclusively established.
http://en.wikipedia.org/wiki/Buffalo,_New_York