State of the Octoraro Creek Watershed

The northwestern parts of the watershed drain into the West Branch, which flows from the west into the Octoraro Reservoir.

West Branch Octoraro Watershed Facts: Population (2020 Census): 7,760 Drainage Area: 48 sq. mi. Stream Miles: 75

Map: West Branch Octoraro Creek Watershed and Subwatersheds.

The northeastern parts of the watershed drain into the East Branch, which flows into the northern part of the reservoir.

East Branch Octoraro Watershed Facts: Population (2020 Census): 16,770 Drainage Area: 91 sq. mi. Stream Miles: 153

Map: East Branch Octoraro Creek Watershed and Subwatersheds.

The mainstem flows from the reservoir approximately 12 miles downstream into the Susquehanna River, below the Conowingo Dam in Maryland.

Mainstem Octoraro Watershed Facts: Population (2020 Census): 20,500 Drainage Area: 72 sq. mi. Stream Miles: 145

Map: Mainstem Octoraro Creek Watershed and Subwatersheds.

Most of the watershed as a whole (pie chart below) is dominated by cultivated land, which includes cropland and pasture and hay fields. Not surprisingly, cultivated land also dominates the smaller drainage areas of most sampling sites (table at right).

Land use patterns were similar across all three branches, but the West Branch had the most cultivated land. The mainstem had the most forested land as well as the most developed land.

There are more than 49,000 miles of streams throughout the Susquehanna River Basin. Agriculture is the top source of stream impairment, affecting recreation (6,653 miles), aquatic life (4,344 miles), and potable water supply (43 miles). The map to the right shows that stream impairments from agriculture are largely concentrated in the southeastern portion of the basin. As discussed above, the Octoraro Creek Watershed is dominated by agricultural land use.

Throughout the Octoraro Creek Watershed, 279 miles of 375 total stream miles are listed as impaired, with 277 impaired miles in PA and 2 impaired miles in MD. Agriculture was the top pollution source affecting aquatic life, followed by various sources grouped into a "development" category. It is important to note that due to multiple source impairments per stream reach, summing individual impairment miles by source category will not equal total impaired stream miles. For example, near Oxford on the Octoraro Creek Watershed map at right, “Aquatic Life - Agriculture” impairments (shown in green) overlap with “Aquatic Life - Development” impairments (red).

While both PADEP and MDE perform intensive assessments of impaired stream miles, the two states differ on methods and reporting to determine impairment and attaining level: Pennsylvania assesses individual stream segments using single data points occurring at targeted sampling sites, and Maryland assesses watersheds (HUC8s) using randomly selected sites and statistical analysis of all data collected throughout the watershed. Refer to the individual state integrated report mapping results for more information.

Most of the stream miles upstream of the sites the Commission sampled were impaired for aquatic life (93%, see pie chart below).  

Siltation and nutrients were the top causes affecting aquatic life, with 86% of sampled sites impaired from siltation and 64% of sites impaired from nutrients. Sources of siltation were mostly agriculture but also development (non-construction related runoff and urban runoff/storm sewers). All nutrient impairments came from agricultural sources.

Other causes of impairment across sampling sites include habitat alteration (other than hydromodification), temperature, and unknown causes from both agriculture and development.

When large amounts of algae die, their decomposition consumes oxygen from the water faster than it can be replenished through photosynthesis or atmospheric mixing. Frequent and reoccurring depletions in oxygen can lead to "dead zones" in the Chesapeake Bay, where oxygen is too low to support aquatic life.

Video: Learn more about how scientists identify and track HABs through this video from the Chesapeake Bay Program. Click the play button on the lower left to view. If the video does not display, click  here to watch on Vimeo. 

Dead zones not only have ecological impact on the wildlife that live in these areas such as seagrass, migratory fish, and blue crabs, but they can have economic impacts affecting communities and fishermen that rely on healthy, thriving ecosystems to support their ways of life.

To learn about other issues that affect the Chesapeake Bay and how you can help, visit the  Chesapeake Bay Program’s website .

In the Octoraro Creek Watershed, the Commission has conducted HABs research on the Octoraro Reservoir including monitoring of high-frequency water chemistry and chlorophyll data collected from a deployed sonde attached to a buoy in the lake. Combined with remote-sensing technology, the Commission is hoping to create a predictive tool for anticipating potential HAB blooms (see technical report at right).

To better manage the Chesapeake Bay and protect and restore its waters, multiple partners across the watershed signed the Chesapeake Bay Watershed Agreement in 2014. The goal is to provide clean water to all who live and rely on the Chesapeake Bay by significantly reducing upstream nutrient input to the Bay. This initiative, with input submitted by residents, fisherman, academic institutions, and local governments, aims to support environment and economic concerns of all stakeholders involved.

Image: This marker stands at the point where the Susquehanna River enters the Chesapeake Bay in Havre de Grace, MD. (J. Zimmerman).

Since the Susquehanna River provides 50% of freshwater to the overall Chesapeake Bay and 90% of freshwater to the Upper portion of the Bay, tracking nutrient and sediment export is an important part of monitoring the current and future health of the Bay. To help with this, Total Maximum Daily Loads (TMDLs) have been established for each state in the Chesapeake Bay Watershed to achieve key nutrient and sediment reductions. States must have programs and projects implemented by 2025 that will reduce N export to target levels. Pennsylvania aims to reduce its watershed nitrogen (N) export by 30 million pounds and New York by 10 million pounds.

Image: Cows along a tributary to the West Branch Octoraro Creek.

Line graphs showing trends for TN yield, loads, and concentrations for the two Lancaster County rivers similar to Octoraro Creek are shown at right. The Conestoga River site has the longest record (from 1985-2022) and shows that TN concentration has been decreasing over time. In the past 16 years, all three sites have had relatively similar TN concentrations and similar TN yields. However, the Conestoga River Watershed contributes the most TN to the Susquehanna River because of its larger drainage area.

From 2018-2022, monitoring equipment recording data every 15 minutes was installed in upstream portions of the West Branch and East Branch Octoraro Creeks. In the summer of 2022, this monitoring equipment was moved farther downstream on each of the branches and transmits real-time data from both the East Branch Octoraro Creek at Street Road and West Branch Octoraro Creek near White Rock, PA.

Website: Real-time 15-minute data can be accessed on the CIM Portal recent results webpage shown at right.