Article

Stream Life at Rock Creek Park

A wide stream with large rocks surrounded by trees.
Rock Creek downstream of Dumbarton Oaks.

U.S. National Park Service

Scientists working with the National Capital Region Inventory & Monitoring Network (NCRN I&M) monitor the health of fish and macroinvertebrate communities in eleven streams at Rock Creek Park. These include Battery Kemble Run, Broad Branch, Dumbarton Oaks, Fenwick Branch, Klingle Valley, Luzon Branch, Normanstone Branch, Pinehurst Branch, Piney Branch, Reservation 630, and Rock Creek Downstream of Dumbarton Oaks. They assess stream fish and macroinvertebrates using the Fish Index of Biotic Integrity and the Benthic Index of Biotic Integrity. These scoring systems take into account the number of taxa; abundance of individuals; and the proportion of taxa that are sensitive, intermediate, or tolerant to disturbance; as well as comparisons with biological communities expected in environments like Rock Creek's. Scientists also collect data on the physical characteristics of these streams to assess the habitat they provide.

Rock Creek Park is located in the Piedmont physiographic province and is surrounded by urban development. The park is made up of forests, streams, and wetlands, as well as recreational land like tennis courts and a golf course.

Map showing location of biological stream survey sites and rivers and streams at Rock Creek Park.
Stream monitoring locations at Rock Creek Park.

Fish Community

A long brown eel with its tail folded to fit in a small aquarium
American eel (Anguilla rostrata) was the most abundant fish species at Rock Creek Park.

U.S. National Park Service

Fish Index of Biotic Integrity

Fish Index of Biotic Integrity (FIBI) scores varied at Rock Creek Park. Five streams received very poor scores, and Broad Branch and Dumbarton Oaks had the lowest possible FIBI score (1). With a score of 3 (fair), Reservation 630 had the highest FIBI of all the streams. Several streams experienced little or no change in FIBI since the previous monitoring cycle. Klingle Valley showed the greatest improvement in FIBI score, increasing from 1.3 to 2.3, while Piney Branch had the greatest decline of 3.3 to 2.

FIBI scores use data such as the abundance of fish that are disturbance tolerant, insect-eating, omnivorous, or benthic to assess stream health. Scores range from 1 to 5, with four possible ratings: very poor (1–1.99), poor (2–2.99), fair (3–3.99), and good (4–4.99). Figure 1 shows the FIBI scores for each stream site.

A bar plot showing Fish Index of Biotic Integrity, ranging from 1 to 5, on the y axis, and Rock Creek Park stream names on the x axis. Refer to narrative figure description for more details.
Figure 1. Fish Index of Biotic Integrity (FIBI) scores for 11 streams at Rock Creek Park. Scores are measured on a scale of 1 to 5, categorized as: 1–1.99 = very poor, 2–2.99 = poor, 3–3.99 = fair, 4–4.99 = good. Missing bars indicate that a stream was not sampled in that year.

Species Found

In 2019 and 2022, 21 species of fish were observed in Rock Creek Park across 11 stream sites. Species richness at most Rock Creek Park streams did not change much since 2008–09. The greatest change occurred at Piney Branch, where the number of species decreased from 13 to 6.

American eels (Anguilla rostrata) were the most abundant fish observed overall (130 total individuals) and were found in nine of the 11 stream sites. They were the most abundant species at Klingle Valley, Piney Branch, and Rock Creek Downstream of Dumbarton Oaks, and the only species recorded at Battery Kemble Run. The blacknose dace and spotfin shiner, despite declining at most sites, were still among the most common fish species at Rock Creek Park.

Multiple sensitive fish species were found in Rock Creek Park streams including: spottail shiner, swallowtail shiner, satinfin shiner, fallfish, and shield darter. Spottail shiner was the most abundant fish species at Fenwick Branch, which had the greatest number of sensitive fish species. Sensitive fish were found in smaller numbers at Broad Branch, Pinehurst Branch, Piney Branch, and Rock Creek Downstream of Dumbarton Oaks.

A tan fish with brown vertical stripes along its side in a small aquarium being measured with a ruler
Juvenile smallmouth bass

U.S. National Park Service

One game fish, a smallmouth bass, was found at Rock Creek Downstream of Dumbarton Oaks. One game fish was also recorded in the park during the 2008–09 monitoring cycle: a largemouth bass at Piney Branch.

Fish Species Tables

Battery Kemble Run Fish Species
2022 FIBI: 2.3 (poor) 

Species # of Individuals Observed
American eel (Anguilla rostrata) 36

Click panels below to see data for other streams.

Macroinvertebrate Community

Like fish, macroinvertebrates are water quality indicators. Some taxa, such as certain types of dragonflies, worms, and non-biting midges, can tolerate poor environmental conditions. Others, including mayflies, stoneflies, and caddisflies, are more sensitive to higher temperatures and pollution levels.
In addition, macroinvertebrates are a major food source for other aquatic animals. Most fish would not be able to survive without them.

Seven worm-like insects of different colors (red, white, brown) with segmented bodies underwater
Larval midges in the Chironomidae family, which includes the genera Cricotopus and Orthocladius, the most abundant macroinvertebrate taxa at Rock Creek Park.

© David H. Funk. / Stroud Water Research Center

Benthic Index of Biotic Integrity

Benthic Index of Biotic Integrity (BIBI) at Rock Creek Park was very poor at every stream, except for Broad Branch which received a poor score. Luzon Branch received the lowest possible BIBI score of 1. BIBI did not change greatly from the previous monitoring cycle at most sites. The greatest improvement in BIBI occurred at Broad Branch, where the score increased from 1.67 to 2.36. Fenwick Branch and Normanstone Branch experienced the greatest declines in BIBI.

Like FIBI, BIBI scores are used to evaluate stream health and take into account the tolerance and abundance of macroinvertebrate taxa, as well as the way each organism feeds and its habitat. BIBI scores range from 1 to 5, with four possible ratings: very poor (1–1.99), poor (2–2.99), fair (3–3.99), and good (4–4.99). Figure 2 shows the BIBI scores for each stream site.

A bar plot showing Fish Index of Biotic Integrity, ranging from 1 to 5, on the y axis, and Rock Creek Park stream name on the x axis. Refer to narrative figure description for more details.
Figure 2. Benthic Index of Biotic Integrity (BIBI) scores for 11 streams at Rock Creek Park. Scores are measured on a scale of 1 to 5, categorized as: 1–1.99 = very poor, 2–2.99 = poor, 3–3.99 = fair, 4–4.99 = good. Missing bars indicate that the stream was not sampled in that year.

Taxa Found

In 2019 and 2022, 59 benthic (bottom-dwelling) macroinvertebrate taxa were observed across 11 stream sites. The most common macroinvertebrates overall were Cricotopus/Orthocladius (both taxa of tolerant non-biting midges), which accounted for 26.5% of all taxa identified.

Cricotopus and Orthocladius are both in the family Chironomidae. While they are often recorded separately, at times the two are grouped together in one category due to challenges identifying aquatic macroinvertebrates to the genus level. Individuals recorded as Cricotopus or Orthocladius were identifiable; those recorded as Cricotopus/Orthocladius were not.

Other types of non-biting midges were also dominant at Rock Creek Park streams, including Eukiefferiella, Diamesa, and Chironomus. None of the common taxa at Rock Creek Park streams were sensitive to environmental disturbance.

Macroinvertebrate community composition (the different taxa present) at Rock Creek Park has shifted since the previous monitoring cycle. At several sites, some of the most common taxa were recorded for the first time in 2019 or 2022. For example, the two most common taxa at Piney Branch, Chironomus (non-biting midges) and Physella (a genus of freshwater snails), were both first recorded at the stream in 2019. At the same time, some taxa that were common in 2008 and 2009 were recorded less frequently in the most recent monitoring cycle. Enchytraeidae (aquatic earthworms) was the most common taxon at Klingle Valley in 2014, accounting for over half of macroinvertebrates recorded at the stream that year, but was not recorded in 2019.

Macroinvertebrate Taxa Tables

Battery Kemble Run Macroinvertebrate Taxa 
Table shows five most common taxa of 21 total found
2022 BIBI: 1.25 (very poor) 

Taxon % of Total Individuals
Diamesa  41.1
Orthocladius  23.3
Cricotopus  10.4
Oligochaeta  4.0
Tvetenia  3.0

Click panels below to see data for other streams.

Stream Physical Habitat Monitoring

Observations of stream physical habitat are gathered at the same location and time as macroinvertebrate monitoring in spring and fish monitoring in late summer. The physical habitat characteristics fall into two broad categories: solid substrates (stream bed materials), and stream flow and depth.

Solid Substrates

  • Embeddedness of substrates: higher embeddedness = less available habitat for small fish, macroinvertebrates, and periphyton (small surface-growing organisms)
  • Epifaunal substrate: the amount and variety of hard materials that can be used as habitat
  • Instream habitat quality: higher values = greater variety of habitat and substrate particle sizes

Stream Flow and Depth

  • Pool quality: diversity of slow- and still-water habitats. Higher scores = more optimal habitat
  • Riffle quality: depth and complexity of riffles (shallow flows disrupted by substrate)
  • Water velocity and depth: higher scores indicate greater variety of water speeds and depths

All characteristics except embeddedness of substrates are measured on a scale of 0–20, with 20 being the most optimal habitat conditions. Embeddedness is measured as a percent.

NCRN I&M no longer reports index scores for stream physical habitat but instead provides data on individual measures. These, along with FIBI and BIBI, provide a comprehensive view of stream quality. Other stream physical habitat characteristics observed but not reported here include the quantity of woody debris and root wads in the stream, stream bank stability, percent of channel shaded, distance from nearest road (remoteness), and land cover composition (percent urban, forested, and agricultural land).

Klingle Valley, Luzon Branch, Pinehurst Branch, and Normanstone Branch had the most favorable habitat quality scores; each characteristic was optimal or suboptimal (Figure 3). Reservation 630 generally had the lowest habitat quality scores, receiving poor or marginal scores for every characteristic.

Embeddedness, a measure of habitat availability that is closely related to epifaunal substrate, also varied between streams. All streams had an embeddedness below 55%, which is considered suitable for most fish and macroinvertebrates (Figure 4).

Eleven bar plots showing stream physical habitat quality scores, ranging from 0–20, on the y-axis for eleven streams at Rock Creek Park. Refer to narrative figure description for more information.
Figure 3. Stream physical habitat characteristics of Rock Creek Park streams in 2008–09 and 2019–22. Epifaunal substrate, instream habitat, pool quality, riffle quality, and velocity/depth are all measured on a scale of 0–20, categorized as: 0–5 = poor, 6–10 = marginal, 11–15 = suboptimal, 16–20 = optimal.

A bar plot showing embeddedness as a percent at eleven Rock Creek Park streams listed along the x-axis, with 0 percent at the top of the y-axis and 100 percent at the bottom. Refer to narrative figure description for more details.
Figure 4. Embeddedness at Rock Creek Park streams in 2008–09 and 2019–22. Embeddedness is a percent; values above 55% indicate less available habitat and poor habitat quality.

Conclusions: Very Poor Macroinvertebrate Communities, Fish Communities and Habitat Quality Vary

Rock Creek Park streams had low BIBI scores, meaning macroinvertebrate communities in the park generally indicate poor stream health. Cricotopus/Orthocladius, two types of tolerant non-biting midges, became far more dominant at most streams, perhaps due to declining stream conditions.

FIBI varied more than BIBI. Sensitive fish species were found in multiple streams. However, Reservation 630 was the only stream with a fair FIBI score. All other sites had poor or very poor scores, further highlighting potential stream degradation.

Stream physical habitat characteristic scores varied widely and did not seem to be strongly related to FIBI or BIBI. Several streams scored fair or good in stream physical habitat characteristics, including some with very poor FIBI and BIBI scores, like Luzon Branch and Pinehurst Branch. Most streams had fairly low embeddedness, indicating sufficient habitat availability.

Learn More about the National Park Service's Inventory & Monitoring Efforts

To help protect natural resources ranging from bird populations to forest health to water quality, National Park Service scientists perform ecological Inventory & Monitoring (I&M) work in parks across the country. The National Capital Region Network, Inventory & Monitoring program (NCRN I&M) serves national parks in the greater Washington, DC area. Visit the NCRN stream biota monitoring webpage to learn more. Previous cycles of fish, macroinvertebrate, and stream physical habitat monitoring were reported in 2012 and 2013.

Part of a series of articles titled Stream Biota Monitoring in the National Capital Region.

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Last updated: December 1, 2025