Maryland Biological Stream Survey

Results of the Round 3 Maryland Biological Stream Survey (2007-2009)

The Maryland Biological Stream Survey (MBSS) is a statewide survey led by the Maryland Department of Natural Resources (DNR). It is a comprehensive program to assess the status of biological resources in Maryland's non-tidal streams; quantify the extent to which acidic deposition affects critical biological resources in the state; examine which other water chemistry, physical habitat, and land use factors are important in explaining stream conditions; provide a statewide inventory of stream biota; establish a benchmark for long-term monitoring; and target future local-scale assessments and mitigation measures needed to restore degraded biological resources.

Following pilot and demonstration projects in 1993 and 1994, the MBSS began its first "round" of sampling to characterize stream conditions and inventory resources statewide. While the MBSS monitors Maryland streams every year in support of multiple objectives, each statewide round of sampling focuses on random sites that provide probability-based estimates of conditions and resources with known confidence. These estimates are computed for the entire state as well as small geographic regions and watersheds. Round 1 of the MBSS was conducted in 1995-1997 and Round 2 was conducted in 2000-2004.


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The following paragraphs report the results of Round 3 of the MBSS which was conducted in 2007-2009. Unlike the previous rounds, which were reported as a single volume (Round 1) or multiple volumes (Round 2), Round 3 results are reported as answers to the important questions, one each to a web page. It is hoped that this format will make the results accessible to a wider audience and increase the understanding of Maryland's streams.


A complete copy of this MBSS Round 3 information can be downloaded and printed as a pdf (10.3 MB).

For a summary of the results, continue below.


This summary distills the results of Round 3 of the MBSS which was conducted in 2007-2009. We encourage you to visit the individual sections of this report to obtain more detailed information.

1. How Many Streams Are in Maryland?

There are 9,203 miles of wadeable, mostly pernnial streams in Maryland comprising 16,300 acres, as well as an equal or greater number of smaller and intermittent streams. Since 1995, 2,271 randomly selected sites have been sampled, meaning that crews have directly sampled 106 miles (or 1.2%) of all wadeable streams in Maryland. It is critical to understand that the random nature of the MBSS survey design allows the entire wadeable stream system (100%) to be assessed by extrapolating site results to provide statistically valid estimates of conditions (with known confidence) statewide, as well as by basin, county, or watershed. Round 3 of the MBSS sampled 252 stream sites and assessed the condition of streams by basin and statewide.

A complete copy of this MBSS Round 3 information can be downloaded and printed as a pdf (10.3 MB).

2. How Is Stream Condition Measured?

The MBSS uses a robust suite of indicators, as well as direct measurements and species accounts, to assess the condition of Maryland’s freshwater, non-tidal streams. These indicators meet the Clean Water Act requirement to address all three elements of water quality: physical, chemical, and biological integrity. Biological integrity is the best indicator of the overall condition of streams, while physical and chemical integrity provide evidence of specific stressors (e.g., low dissolved oxygen). The MBSS has developed and currently implements the following reference-based indicators:

  • Fish Index of Biotic Integrity (IBI)
  • Benthic Macroinvertebrate IBI
  • Combined Biotic Index
  • Physical Habitat Index

A complete copy of this MBSS Round 3 information can be downloaded and printed as a pdf (10.3 MB).

3. What Is the Condition of Streams in Maryland?

Round 3 (2007-2009) of the MBSS has assessed the condition of streams both (1) statewide and (2) by 12 major drainage basins that drain to the Chesapeake Bay (Tributary Strategy Basins) or the Ohio River (Youghiogheny River Basin) or the Atlantic Ocean (Ocean Coastal Basin). Statewide the percentages of streams in good, or minimally degraded, condition are

  • 34% using the Fish IBI.
  • 29% using the Benthic IBI.
  • 23% using the CBI.
  • 14% using the PHI.

A complete copy of this MBSS Round 3 information can be downloaded and printed as a pdf (10.3 MB).


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4. What Is the Trend in the Condition of Streams in Maryland?

The MBSS is designed to detect trends in stream condition in three ways:

  • Changes across multiple-year rounds of statewide sampling
  • Annual changes in statewide assessments
  • Annual changes at fixed sentinel sites

Statistical standards for trends detection generally require five points in time; therefore only visual comparisons across the three rounds of statewide assessment can be made. Both the benthic and fish indices of biotic integrity (IBIs) show a variable, but consistent, relative proportion of stream miles in each condition class for each major drainage basin. Statewide the percentage of stream miles in good condition increased by 5-7% from Round 1 to Round 3, while the percentage of stream miles in very poor condition decreased by a comparable amount. The graph below shows the annual statewide assessment of degraded non-tidal streams in Maryland


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A complete copy of this MBSS Round 3 information can be downloaded and printed as a pdf (10.3 MB). ​​​​

5. What Factors are Degrading Maryland Streams?

The MBSS collects data on a wide range of stressors that degrade streams. The degradation of streams in Maryland results from both the importance (or severity) and the prevalence (or extent) of each stressor. Acid mine drainage and low dissolved oxygen have the most severe effects on fish and macroinvertebrates benthos, respectively. The relative extent of each of 10 major stressors is shown for each Maryland tributary basin, and statewide, in the graph below.




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This report on Round 3 results answers the following questions about stressors in detail:

  • Has the number of acidic and acid-sensitive streams in Maryland increased or decreased since 1995 and what are the sources?
  • What impacts do nutrients and sediment have on Maryland streams?
  • How warm are Maryland streams?
  • How many Maryland streams have natural stream channels (not channelized)?
  • How many Maryland streams have adequate vegetated riparian buffers?
  • How many miles of Maryland streams have at least one non-native fish species?

A complete copy of this MBSS Round 3 information can be downloaded and printed as a pdf (10.3 MB).

6. Where Are the Best and Worst Condition Streams in Maryland?

Streams in Maryland vary from those in very good condition (minimally disturbed by human activities) to those in very poor condition. To better appreciate this wide range of condition, we shown the streams sampled in Round 3 of the MBSS that represent the best and worst conditions sampled from 2007-2009.


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A complete copy of this MBSS Round 3 information can be downloaded and printed as a pdf (10.3 MB).

7. How Are Maryland’s Fish Doing?

Maryland has a diverse freshwater fish fauna including 96 species living across the Highlands, Eastern Piedmont, and Coastal Plain regions of the state. The MBSS provides a robust inventory of the distribution and abundance of Maryland fishes based on estimates from its probability-based design. It also provides critical information on the status of Maryland fishes, such as the following:

  • In the Coastal Plain, eastern mudminnows and American eels are each found in about 2 out of every 3 streams. Blacknose dace are the most common fish in the other regions, occurring in 90% of both East Piedmont and Highlands warmwater streams and nearly half of all Highlands coldwater streams. The Coastal Plain has the most fish species (60), compared to the East Piedmont (55 species), the Highlands warmwater (46 species), or the Highlands coldwater streams (24 species).
  • The Maryland fishes most sensitive to pollution are sea lamprey, central stoneroller, comely shiner, common shiner, fallfish, ironcolor shiner, Blue ridge sculpin, mottled sculpin, flier, banded darter, shield darter, and swamp darter, while the fishes least sensitive to pollution are blacknose dace, bluntnose minnow, creek chub, golden shiner, bluegill, green sunfish, largemouth bass, pumpkinseed, and tessellated darter.
  • There are 9 species of freshwater game fish found in Maryland and the MBSS has recorded the lengths of more than 6,000 individual game fish. Brook trout, followed by smallmouth and largemouth bass, were most commonly collected. Surprisingly, more game fish were collected in first order streams (defined as first-order because they have no upstream tributaries) than in any other size stream. This argues for increased protection of these small streams for recreational as well as ecological reasons.
  • The ability of Maryland DNR to conduct effective stream biodiversity conservation has been substantially improved from the inventories of aquatic species that MBSS has collected. Specifically, protection of rare species, like the blackbanded sunfish or dwarf wedgemussel, and efforts to control non-native species, like the rusty crayfish and Oriental weatherfish, would not have been possible without this information.
  • Maryland DNR monitoring has demonstrated that the iconic brook trout live in fewer streams than they did 30 years ago. Specifically, surveys by the Fisheries Service and MBSS have documented the loss of brook trout from several central Maryland streams since that time. These losses were coincident with urban development in every case, with pavement covering less than 5% of the drainage area of a stream typically sufficient to eradicate brook trout.
  • The American eel has a unique, catadromous life history that spawns in the tropical Atlantic Ocean and grows to maturity in estuarine and freshwater habitats. Juvenile eels (or elvers) must migrate upstream. The construction of more than 1,000 man-made barriers to migratory fish ​in Maryland have reduced access of American eel and other fish to their historical habitats. It is likely that the American eel was abundant in virtually all the estuaries, rivers, streams, and lakes of Maryland and other coastal states prior to the colonization of North America. Today, MBSS data from Round 3 shows the obvious absence of individuals in areas above dams. American eels were found at only a few sites sampled above the Fall Line.


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A complete copy of this MBSS Round 3 information can be downloaded and printed as a pdf (10.3 MB).

8. How Are the Other Freshwater Animals in Maryland Doing?

The electrofishing and visual searching of streams by the MBSS records many animals other than fish, such as frogs, toads, salamanders, turtles, snakes, lizards, mussels, and clams. In addition, the MBSS conducts systematic searches of the riparian zone adjacent to the stream for seasonal (or vernal) pools and notes the animals seen or heard in these pools. The MBSS found 42 species of amphibians and reptiles and 8 species of shellfish (including 5 rare mussels) living in Maryland’s freshwater streams. The most common are the northern green frog (in the Coastal Plain and Highlands) and the two-lined salamander (in the Eastern Piedmont). The Coastal Plain region generally has more amphibian and reptile species (35) than either the Eastern Piedmont or Highlands, each of which have 20 species. The presence of seasonal pools increases in the more eastern and southern basins of Maryland as shown in the map below.


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