IES has measured precipitation acidity in the area since 1984. Rainfall in the area has an average pH of 4.27, with averages falling to 4.00 in July but rising to 4.54 in November. This means the rain in Dutchess County and the watershed is ten times more acidic than the natural 5.2 reading for precipitation. River modifications There are 13 dams along the creek. Five are located in Beacon, most built to serve past industry there (one is still used for hydroelectric power generation. The highest, near the city's downtown section, is tall. Three are in Beekman and two are in Fishkill, the latter built by Texaco for a research facility it ran in the area from 1931 to 2003. The dams along the upper Fishkill impound the stream into old mill ponds, such as Furnace Pond in Tymor Park, just above the site of an old iron smelter, giving the pond its name. The dams prevent the upstream movement of fish at all stages of the creek. The oldest extant bridge over the creek is Tioronda Bridge, just above its estuary in Beacon. It was an iron bowstring truss bridge built shortly after the Civil War that carried South Avenue across the Fishkill. It was listed on the National Register of Historic Places in 1976, but it had deteriorated so much that by the end of the 20th century it had been closed even to pedestrians. In 2006 the city dismantled it, preserving the bowstring trusses for possible reuse on a rebuilt bridge. The abutments remain in the stream, carrying some utility pipes only. Wildlife The creek and its watershed support a great diversity of species. As a fishery, it is stocked with brown trout, and has a significant brook trout population as well. The estuary supports a largemouth and smallmouth bass population. Some plant and animal species found near the creek and in its watershed are on the state list of endangered or threatened species. The former include the bog turtle, wild hydrangea and live-forever. Threatened species in the creek and watershed include the bald eagle, Blanding's turtle, least bittern, pied-billed grebe, stiff-leaf goldenrod, swamp cottonwood and blazing star. Several salamander and turtle species are also species of concern. Eurasian watermilfoil, an invasive species, has been seen in some areas. Geology The creek flows through two distinct geological regions within the Highlands: the Mid-Hudson Valley and the Hudson