View in Vital Signs- Healthy Water Quality
- Freshwater
- Indicator
- Freshwater Benthic Index of Biotic Integrity
- Vital Sign Indicator
- Percent (%)
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No targets are currently set for this indicator.
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Kate Macneale
- Contributing Partners
- Last Updated
- 09/05/2023 08:25:23
The Benthic Index of Biotic Integrity (B-IBI) describes the biological condition of stream sites and their surrounding habitat based on the diversity and relative abundance of the benthic (bottom dwelling) macroinvertebrates found at the site. Ten measures of biological condition are scored and summarized as the B-IBI, which ranges from a score of 0, indicating very poor stream condition, to 100, indicating excellent condition.
Macroinvertebrate samples were collected from 718 sites across Puget Sound in the last five years (2018-2022). Each site is characterized as Very Poor, Poor, Fair, Good, or Excellent based on its average B-IBI score.
Stream-dwelling organisms are a useful indicator of water quality and can help describe the biological condition of stream sites and the surrounding habitat. Macroinvertebrates vary in their tolerance to environmental stressors; some are quite sensitive and cannot thrive outside pristine environments, while others are tolerant of change. Thus, the abundance and types of macroinvertebrates found in a stream reflects the overall stream condition.
- Stream conditions are mixed across Puget Sound. The biological condition category at 718 sites ranged from excellent or good (41 percent) to fair (22 percent) to poor or very poor (37 percent).
- Over time, most B-IBI scores have either improved or remained stable. Analysis of trends at 188 sites with at least 10 years of monitoring data show that B-IBI scores improved at 22 percent of sites and declined at only 2 percent of sites. Scores at three-quarters of sites (76 percent) have not changed significantly over time.
- Overall, these trends are encouraging. While development has increased in the region, stream health appears to have improved in more than one of five streams and declined in only one of 50 streams. This may be due in part to stream and riparian restoration as well as historic and ongoing actions that aim to control and treat stormwater (see the Stormwater Strategic Initiative for more information).
- Monitoring Program
King County Benthic Index of Biotic Integrity for King County Streams
Washington State Department of Ecology Stream Biological Monitoring
- Data Source
The Benthic Index of Biotic Integrity (B-IBI) monitors the diversity and relative abundance of the benthic (bottom dwelling) macroinvertebrates found in Puget Sound streams. These macroinvertebrates include aquatic insect larvae, such as mayflies, stoneflies, caddisflies, beetles, flies, and dragonflies, as well as worms, snails, and many other invertebrates.
The B-IBI combines 10 metrics of stream biology, such as taxa diversity and the presence of invertebrates that are tolerant and intolerant to pollution. The ten measures are combined and summarized as a single B-IBI score, which ranges from a value of 0 to 100. B-IBI scores are translated into the following five biological condition categories:
Biological Condition Description B-IBI Score Excellent Comparable to least disturbed reference condition; overall high taxa diversity, particularly of mayflies, stoneflies, caddisflies, long-lived, clinger, and intolerant taxa. Relative abundance of predators high. 80-100 Good Slightly divergent from least disturbed condition; absence of some long-lived and intolerant taxa; slight decline in richness of mayflies, stoneflies, and caddisflies; proportion of tolerant taxa increases. 60-80 Fair Total taxa richness reduced - particularly intolerant, long-lived, stonefly, and clinger taxa; relative abundance of predators declines; proportion of tolerant taxa continues to increase. 40-60 Poor Overall taxa diversity depressed; proportion of predators greatly reduced as is long-lived taxa richness; few stoneflies or intolerant taxa present; dominance by three most abundant taxa often very high. 20-40 Very Poor Overall taxa diversity very low and dominated by a few highly tolerant taxa; mayfly, stonefly, caddisfly, clinger, long-lived, and intolerant taxa largely absent; relative abundance of predators very low. 0-20 See the Puget Sound Stream Benthos B-IBI page for more information about the B-IBI scoring system.
Many local jurisdictions, tribes, state and federal agencies, as well as community groups in Puget Sound routinely collect and report B-IBI data. For instance, the Washington State Department of Ecology samples 50 randomly selected stream and river sites every four years to get an unbiased estimate of regional conditions. Counties, cities, tribes and community groups also sample stream sites throughout Puget Sound to characterize the status and trends in stream condition.
Macroinvertebrate samples were collected from 718 sites across Puget Sound in the last five years (2018-2022). We characterize biological condition at each site based on the average B-IBI score.
We analyzed trends in B-IBI scores from 188 sites that have been monitored for at least 10 years from 1994 through 2022. To ensure samples were comparable across time, taxonomic data were standardized to a coarse (historic) level and B-IBI scores were calculated using R. Trends results are based on Mann Kendall tests, with significance determined by alpha=0.05. Samples with fewer than 450 identified organisms were excluded from the analyses.
- Critical Definitions
Benthic refers to organisms found on, among, or within the bottom of a body of water.
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Macroinvertebrate communities are impacted by a variety of stressors that are associated with land use conversion and urbanization, including but not limited to excessive fine sediment, contaminants in stormwater runoff, loss of riparian vegetation and scouring high flows. Thus, improvements in B-IBI scores are presumably due to reductions in these environmental stressors, however, it is difficult to point to specific actions. Over the last several decades, land use conversion has continued and urbanization has intensified, and yet macroinvertebrate communities appear to be recovering in many streams across the region. Studies are underway to fully understand how conditions have been improved over time, and whether credit can be given to changes in stormwater best management practices and stream and riparian restoration.
The Stormwater Strategic Initiative includes a Freshwater Quality Implementation Strategy which aims to improve water quality through integrated watershed planning and capacity building. The strategy outlines a series of actions, approaches, and interim results that are meant to reverse some of the impacts changes in land use have had on rivers and streams throughout the Puget Sound.
The "Restoration and Protection of Select Puget Lowland Stream Basins” project is a phased effort aiming to restore and protect streams throughout Puget Sound. The Stressor Identification and Recommended Actions for Restoring and Protecting Select Puget Lowland Stream Basins report is the second of five phases. The goal of this phase is to identify human activities that are impacting a select group of streams and recommend actions to facilitate restoration and protection within the stream basins.
Data from 26 tribes, agencies and non-profit groups have contributed to this update. Such a comprehensive survey of regional B-IBI scores would not be possible without their efforts.
- City of Bainbridge Island
- City of Bellevue
- City of Bellingham
- City of Bothell
- City of Everett
- City of Federal Way
- City of Kirkland
- City of Lake Forest Park
- City of Olympia
- City of Redmond
- City of Sammamish
- City of Seattle
- Clallam County
- King County
- Kitsap County
- Pierce County
- Puyallup Tribe of Indians
- Snohomish County
- Sno-King Watershed Council
- Snoqualmie Tribe
- The Tulalip Tribes
- Thurston County
- University of Washington
- Vashon Nature Center
- Washington State Department of Ecology
- Whidbey Watershed Stewards
No datasets uploaded.
- Reporting Instructions
No Subcategories for this Puget Sound Indicator.