First Stream in Newark was a vital waterway for the founding of the city; it was also known as Mill Brook because it was originally used to power a watermill. It is now completely underground and integrated with the 19th-century combined sewer system, although overflows still have an outlet at the historic mouth of the stream into the Passaic River.
I made these info sheets originally just as a way to tell people about the old streams and the sewers that have replaced them in NYC. I thought it was funny, for information about old streams that no longer existed, to present it as a flyer for a tour that didn't actually exist either. It was only a few years later than I began to develop actual walking tours where I would take people above-ground along the old routes of these streams. We only walk above-ground, but we peer down a few manhole covers along the way so that we can actually see the water flowing below (which is nowadays a mixture of natural groundwater and combined sewage together).