Around 1650, long before Yonkers was established as a city and well before New York became New York, a Dutch lawyer and landowner named Adriaen van der Donck built a water-powered sawmill on Nepperhan Creek, near the spot where that creek flowed out into Hudson River. That sawmill became the center of a growing town on van der Donck’s land. Eventually the town become known as Yonkers, a name that was derived from van der Donck’s Dutch honorific “Jonkheer” (which roughly translates as “gentleman" or "squire”).
The sawmill that Van der Donck built also gave a new name to Nepperhan Creek, and it has known as the Sawmill River ever since. The Sawmill is the Hudson’s longest tributary, at 23 miles long, but it is still a fairly small river, and as Yonkers grew, it grew around and over the small river. As more industrial and residential buildings were built in the 19th century, some straddled the river. Sections of it were shunted through underground flumes, and road bridges were built across other parts of it, until eventually the city decided to simply cover over the last exposed sections of the river. By the early 1900s, the river was completely underground for the half-mile section that passes through downtown Yonkers.