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Health of Freshwater Streams in the Chesapeake Bay Watershed

Between 2000-2010, more than 14,005 sites were sampled and rated for biological integrity.  The average stream health scores in a subset (10,492) of these of these sampling locations indicated that:

  • 4,537 (43 percent) were in fair, good or excellent condition
  • 5,955 (57 percent) were in very poor or poor condition

Health of Freshwater Streams in the Chesapeake Bay Watershed

Get Adobe Flash player Click to launch fullscreen dynamic map

Average 2000-2010 Stream Health in the Chesapeake Bay Sub-watersheds May 29 2013 / Download

Average 2000-2010 Stream Health in the Chesapeake Bay Watershed Jun 25 2012 / Download

April 21, 2011

Brook trout play a critical role in the Chesapeake Bay watershed, but without cool, clean water, the fish cannot survive. Working in headwater states, Chesapeake Bay Program partners are promoting land conservation and habitat restoration as ways to clean up local waterways and conserve the iconic species.
Closed Captions: http://www.youtube.com/watch?v=jWZ5oor1z4A

Produced by Steve Droter
Underwater Footage: U.S. Fish & Wildlife Service
Music: “Mille giraffons (Instrumental)” by Löhstana David

April 21, 2011

Follow biologists as they track native brook trout in western Maryland’s Savage River, and learn why these fish are used to monitor the health of the freshwater streams that flow to the Chesapeake Bay.

Produced by Steve Droter


An effective way to measure the health of freshwater streams and rivers is to study the many tiny creatures that live in these waters. The abundance and diversity of snails, mussels, insects and other bottom-dwelling organisms – known as benthic macroinvertebrates – are good indicators of the health of streams because these creatures can’t move very far and they respond in certain predictable ways to pollution and environmental stresses.

A healthy Bay watershed would have a majority of streams ranked as fair, good or excellent.  Some generalizations about the health of the watershed’s streams can be made:

  • Streams tend to be in very poor to fair condition around large urban areas, such as metropolitan Washington, D.C. Streams in heavily farmed or mined areas are also often in very poor to fair condition.  These land uses stress streams by contributing high levels of pollution and altered stream flow which decrease in-stream and streamside habitat.
  • In contrast, streams tend to be in good to excellent condition in forested areas with ample natural habitat and low levels of pollution, such as in forested areas of the upper James and Potomac rivers and the West Branch of the Susquehanna River.

Healthy freshwater streams are intrinsically linked to a healthy Chesapeake Bay. The watershed’s streams, creeks and rivers eventually flow into the Bay, so their water quality has a direct affect on the entire Bay.  Clean local waterways also support a diversity of fish and wildlife and are essential to residents who use them as a source of drinking water and recreational activities.


In general, it can be said that a healthy Bay watershed would have a majority of streams ranked as fair, good or excellent. The Strategy for Protecting and Restoring the Chesapeake Bay Watershed includes a goal to improve the health of streams so that 70 percent of sampled streams sites throughout the Chesapeake watershed rate fair, good, or excellent as measured by the Index of Biotic Integrity by 2025.

Additional Information

Data Collection for this Indicator

Only data collected in a random design (10,492 sites) were used for the analysis portrayed in the pie chart and the static map that shows average B-IBI ratings in Chesapeake Bay Sub-watersheds.  Of those 10,492 sites, between 2000 and 2010:

  • 13 percent (1,388 sites) were in excellent condition
  • 12 percent (1,305 sites) were in good condition
  • 18 percent (1,844 sites) were in fair condition
  • 15 percent (1,578 sites) were in poor condition
  • 42 percent (4,377 sites) were in very poor condition

An dynamic map, available under the “Map” tab above, portrays data from 14,005 sites (including the 10,492 random sites and 3,513 targeted-sampling-design sites).

Health of streams was evaluated by the Chesapeake Bay Basin-wide Benthic Index of Biotic Integrity (B-IBI), which was developed from benthic macroinvertebrate data collected across the entire Chesapeake Bay watershed.

Most monitoring programs in the Bay watershed collect benthic macroinvertebrate samples with somewhat similar field methods and calculate a common suite of indicators from the data. However, the programs use state-specific protocols to score and evaluate these indicators to identify “impaired” waters for regulatory requirements that are not comparable across state lines.

The purpose of this indicator is to evaluate benthic community health in non-tidal streams and wadeable rivers in a uniform manner and in the context of the entire Bay watershed. The index is one of several Chesapeake Bay Program analytical tools applied to multi-jurisdictional monitoring data for watershed assessments.

  • The index is “reference based,” meaning sampling locations are evaluated according to how similar they are to sites with little or no measured anthropogenic disturbance.
  • Data from multiple stream monitoring programs are incorporated into a common database structure and key family-level metrics (indicators) that indicate the health and abundance of the communities are calculated from the data.
  • The metrics are scored according to their similarity to reference sites in each bioregion (areas with different geomorphologic traits).
  • Index scores are rated on a five-tiered scale: Excellent (67%-100%), Good (50%-67%), Fair (30%-50%), Poor (17%-30%), and Very Poor (0%-17%).

In the 2000-2010 period, some state monitoring programs (most notably Pennsylvania and New York) collected data from many sampling sites identified as “targeted” (such as sites below an outfall of a pollutant source) and these data were not included in the map averaging scores across the watershed to avoid the presumed bias introduced by targeted site data.  Watershed ratings in Pennsylvania and New York are therefore less certain because they are derived from fewer random/systematic sites.

Stream Health

These results show a clear link between the watershed-wide B-IBI scores and land-based activities in individual watersheds.

  • The poorest stream indexes occur in highly urbanized watersheds such as those in the Baltimore-Washington D.C. metropolitan region. Stream health is compromised in urban areas by extreme land disturbance and an abundance of paved surfaces. These stressors result in high levels of pollution, altered stream flow, and poor quantity and quality of streamside vegetation.
  • Lower scores in the Chesapeake Bay basin are also present in areas with intense agricultural activity such as the lower Eastern Shore and south central Pennsylvania. Excess nutrients and sediment compromise stream health in these areas. The Upper West Branch of the Susquehanna River in Pennsylvania appears to be compromised by mining activity which causes habitat alterations and toxic plumes that negatively impact benthic stream populations.
  • The highest B-IBI scores are typically found in minimally disturbed watersheds with low levels of pollution and stable in-stream and streamside habitats. These watersheds tend to be clustered in forested areas of the upper James and Potomac rivers and the West Branch of the Susquehanna River.

Stream and River Pollution

There are many different causes of stream and river pollution across the Bay watershed. Benthic macroinvertebrates are generally harmed by pollutants such as metals, acidity, sediment, pesticides, nitrogen and phosphorus. These pollutants come from sources such as mining, agriculture, urban and suburban runoff, automobile and power plant exhaust, and wastewater treatment facilities.

Additional Water Quality Assessment Reports

This indicator is only one example of stream health assessments.  Indicators, including water quality and physical in-stream and watershed health parameters, are also used by organizations to characterize stream health.

See the following links for information about other selected stream health assessments produced by Bay Program partners:

Future Enhancements

The adhoc workgroup that guided the development of this improved indicator deemed it appropriate for regional assessments of benthic macroinvertebrate health.  The group also identified the following future work to improve upon the indicator:

  • Determine the influence of blackwater systems on B-IBI scores and potentially having a blackwater-specific scoring approach for affected regions
  • Explore the effects of targeted vs. random sites on B-IBI watershed results
  • Develop a limestone-specific scoring approach for affected regions in the Valleys and possibly the Piedmont (more limestone data would need to be incorporated in order to do this)
  • Test the validity of the Coastal Plain index by identifying Reference and Degraded sites in the coastal plain bioregions
  • Calculate the trends in the B-IBI over time with a subset of the data collected from fixed locations
  • Validate the B-IBI with new data as it is added to the database
  • Improve the B-IBI performance in the North Central Appalachians and the North Appalachian Plateau and Uplands regions by acquiring new habitat and water quality data and better identifying Reference and Degraded sites
  • Further compare the several Coastal Plain indexes that have been developed and evaluate if and how they differ when calculated from the same data set
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