Furnace Brook, located in Cortlandt, New York is a small tributary to the mighty Hudson River. As the Hudson River is actually an estuary - and is tidal, so too, are many of the lower elevation tributaries along its many miles. Furnace Brook is one of those tidal rivers or streams, and has many secrets to yield. Hiking the park through which Furnace Brook flows, Oscawana Park, the time of day takes on a different appearance for trails near the river, depending entirely upon the amount of rainfall and where Earth is in the tidal cycle. Things hidden beneath the waters' surface!