Chillisquaque Creek is a tributary of the West Branch Susquehanna River in Montour County and Northumberland County, in Pennsylvania, in the United States. It is approximately long and flows through Derry Township, Washingtonville, and Liberty Township in Montour County and East Chillisquaque Township and West Chillisquaque Township in Northumberland County. The watershed of the creek has an area of . Agricultural impacts have caused most of the streams in the watershed of the creek (including the main stem) to be impaired. Causes of impairment include sedimentation/siltation and habitat alteration. The average annual discharge of the creek between 1980 and 2014 ranged from . Its watershed mainly consists of rolling agricultural land. The creek's channel flows through rock formations consisting of sandstone and shale. It is a warmwater stream.
The watershed of Chillisquaque Creek occupies parts of four counties: Columbia County, Montour County, Northumberland County, and Lycoming County. There is a gauging station along the creek near Washingtonville. A Shawnee village had been established at the confluence with the West Branch Susquehanna River by 1728. A fort known as Fort Bosley also historically existed on the creek near Washingtonville. Numerous bridges were built over the creek in the 19th and 20th centuries, two of which are on the National Register of Historic Places. The creek is designated as a Warmwater Fishery and a Migratory Fishery. It lacks trout, but has in the past been stocked with various other fish species. A tract of the creek's floodplain is known as the Chillisquaque Creek Natural Area and is owned by Bucknell University. Various bird species have been observed near it and woodland wildflowers inhabit the creek's vicinity. Recreational opportunities in the watershed include canoeing and fishing.
Course
Chillisquaque Creek begins at the confluence of East Branch Chillisquaque Creek and Middle Branch Chillisquaque Creek near the northern border of Derry Township, Montour County. It flows west-southwest for a few tenths of a mile before turning south-southwest. After several tenths of a mile, it turns west for a short distance and receives the tributary West Branch Chillisquaque Creek from the right. The creek then turns south-southeast for more than a mile, flowing alongside Pennsylvania Route 54 and crossing it once. In this reach, it briefly flows alongside the western border of Washingtonville before crossing Pennsylvania Route 254 and receiving the tributary Mud Creek from the left. The creek then begins flowing in a roughly west-southwesterly direction and soon enters Liberty Township. It continues flowing in a similar direction in Liberty Township (though it does flow north, west, and then south for several tenths of a mile at one point), flowing through a broad valley with Limestone Ridge on the north and receiving many unnamed tributaries from both sides. After several miles, the creek leaves the valley and crosses Interstate 80. Several tenths of a mile further downstream, it exits Liberty Township and Montour County.
Upon exiting Montour County, Chillisquaque Creek enters East Chillisquaque Township, Northumberland County. It then turns south-southeast for about a mile, flowing close to the county line and crossing Pennsylvania Route 642. In this reach, it receives Beaver Run, its last named tributary, from the left. The creek then turns southwest for a few tenths of a mile before turning south for a similar distance. It then turns west for several tenths of a mile before turning southwest. The creek crosses Pennsylvania Route 45 and meanders in a southwesterly direction for more than a mile, flowing along the border between East Chillisquaque Township and West Chillisquaque Township. It then turns south for a few tenths of a mile, passing the Rishel Covered Bridge as it continues flowing along the border. After this, the creek turns west-southwest, entering West Chillisquaque Township, before turning south and then west. For more than a mile, the creek flows through a valley between Montour Ridge and a smaller hill. Upon leaving the valley, the creek crosses Pennsylvania Route 147 and Pennsylvania Route 405 and heads in a southwesterly direction for several tenths of a mile before reaching its confluence with the West Branch Susquehanna River.
Chillisquaque Creek joins the West Branch Susquehanna River upriver of its mouth.
Tributaries Chillisquaque Creek has five named direct tributaries: Beaver Run, Mud Creek, West Branch Chillisquaque Creek, East Branch Chillisquaque Creek, and Middle Branch Chillisquaque Creek. Beaver Run joins Chillisquaque Creek upstream of its mouth and its watershed has an area of . Mud Creek joins Chillisquaque Creek upstream of its mouth and its watershed has an area of . West Branch Chillisquaque Creek joins Chillisquaque Creek upstream of its mouth. East Branch Chillisquaque Creek joins Chillisquaque Creek upstream of its mouth, as does Middle Branch Chillisquaque Creek. Their watersheds have areas of and , respectively.
Hydrology Reaches of Chillisquaque Creek are designated as an impaired waterbody. Causes of impairment include sedimentation/siltation and habitat alteration, while likely sources include agriculture and industrial point-source discharge. Many streams in the watershed experience significant impacts due to agriculture, as heavy use of agricultural lands reduces the creek's water quality. A total of of streams, or about 83% of all the stream miles in the watershed, are impaired. The nearby Mahoning Creek is in "better environmental shape" than Chillisquaque Creek. However, in the 1980s, the concentrations of pollutants in the creek were relatively low, despite being increased by discharges from a nearby power plant. For instance, the selenium concentration was consistently under 0.010 milligrams per liter, the United States Environmental Protection Agency criterion for that pollutant.
Between 1980 and 2014, the highest average annual discharge of Chillisquaque Creek at Washingtonville was , in 2011. The second-highest average annual discharge, , occurred in 1984, while the third-highest, , occurred in 2004. The lowest average annual discharge, , occurred in 2001. The second-lowest, , occurred in 1988 and the third-lowest, , occurred in 2013. The months with the highest average discharge are March, April, and December; their values are , , and , respectively. The PPL power plant contributes about of water to the creek.
During several measurements in the 1970s, the pH of Chillisquaque Creek near Washingtonville ranged from 6.3 to 7.1. The specific conductance of the creek ranged from 170 to 250 micro-siemens per centimeter at . The turbidity ranged between 2 and 7 Jackson Turbidity Units. The concentration of water hardness in the creek ranged from 84 to 130 milligrams per liter. The concentration of dissolved oxygen ranged from 9.0 to 11.0 milligrams per liter, while the hydrogen ion concentration ranged from 0.00008 to 0.00051 milligrams per liter. The carbon dioxide concentration ranged between 4.7 and 49 milligrams per liter.
In the 1970s, the concentration of nitrate as nitrogen in Chillisquaque Creek near Washingtonville ranged from 1.68 to 2.00 milligrams per liter, while the concentration of nitrite as nitrogen ranged from 0.040 to 0.164 milligrams per liter. The concentration of phosphorus ranged from 0.040 to 0.520 milligrams per liter. The organic carbon concentration was 3.0 milligrams per liter in one measurement. The concentration of sulfate ranged from 32.0 to 114 milligrams per liter in the creek's filtered water and the chloride concentration ranged between 8.0 and 14.0 milligrams per liter, again in filtered water. The ammonia concentration ranged from 0.026 to 0.811 milligrams per liter.
In the 1970s, the concentration of magnesium in Chillisquaque Creek ranged from 1.50 to 9.50 milligrams per liter in the creek's filtered water and the calcium concentration ranged from 26.4 to 48.8 milligrams per liter, in filtered water. The arsenic concentration was once measured to be 77 micrograms per liter. The cadmium, recoverable chromium, and recoverable copper concentrations were each once measured to be less than 3, less than 20, and 30 micrograms per liter, respectively. The recoverable iron concentration ranged from 160 to 410 micrograms per liter. The concentrations of zinc, lead, manganese, and aluminum were less than 20, less than 50, 50, and 500 micrograms per liter, respectively. Additionally, a detectable amount of nickel was observed in the creek.
Geography, geology, and climate
The elevation near the mouth of Chillisquaque Creek is above sea level. The elevation of the creek's source is approximately above sea level. The gradient of the creek is about .
The upper reaches of the watershed of Chillisquaque Creek are in the Muncy Hills. Montour Ridge is located to the south of the watershed. Additionally, Limestone Ridge is situated near the creek. The creek's drainage basin mainly consists of rolling agricultural land, with some forested floodplains. Much of the central part of Montour County is in the 100-year floodplain of the creek and its tributaries. In places, it has high, muddy banks, and is generally "placid", save for some riffles and gravel bars. It is rarely blocked by fences and fallen trees, but there are a few strainers. A seep is located along the creek near the Bucknell preserve and a spring is located below Pennsylvania Route 54.
Chillisquaque Creek cuts a broad and almost flat valley through rock of the Hamilton Group. It is wide and rarely rises to more than higher than the creek. A 1775 map shows the creek's headwaters as being at Tilghmans Springs. However, A. Joseph Armstrong (author of Trout Unlimited's Guide to Pennsylvania Limestone Streams) was unable to find the springs. In 2021, a 1769 survey of the Tilghman estate was obtained from the Pennsylvania Archives by Tyler Dombroski. The 1769 survey indicated the location of Tilghman's Springs as modern day "Blue Springs," just north of Washingtonville Borough where PA Route 54 crosses Chillisquaque Creek. The creek is between wide and has no apparent limestone influence, despite being near Limestone Ridge and flowing through Limestone Township.
Chillisquaque Creek flows in a generally southwesterly direction. The channel of the creek is sinuous and flows through rock formations consisting of sandstone and shale. Oriskany sandstone and Lower Helderberg limestone occur on Limestone Ridge near it. Oriskany cherty sandstone occurs near the confluence of the tributary Mud Creek. Additionally, Black Genesee shales have also been observed near the creek, as does the Tully limestone. Rock of the Hamilton Group is common in the area as well and is in places covered with sandstone boulders of the Pocono Formation. Hydric soils occur along it in central Montour County.
In the early 1900s, the average annual rate of precipitation in the watershed of Chillisquaque Creek was . The creek has relatively warm water.
Watershed
The watershed of Chillisquaque Creek has an area of . The mouth of the creek is in the United States Geological Survey quadrangle of Northumberland. However, its source is in the quadrangle of Washingtonville. The creek also passes through the quadrangle of Milton. The creek can be accessed from Pennsylvania Route 45, Pennsylvania Route 405, and Pennsylvania Route 642.
The watershed of Chillisquaque Creek parts of four counties: Montour County, Northumberland County, Columbia County, and Lycoming County. The portion of Montour County that is in the watershed is the central portion. It is the largest watershed in that county, accounting for 56 percent of its land area. It is also the only large stream in northern Northumberland County. There are about of streams in the watershed.