EcoCheck banner

Browse History: Dissolved Oxygen (2009) | Phytoplankton Index of Biotic Integrity (2009) | Water Clarity (2009) | Water Quality Index (2009)
Indicator Icon Water Quality Index

The Water Quality Index combines the water quality threshold scores (chlorophyll a, water clarity, and dissolved oxygen) into a single overarching index. Good overall water quality is characterized by having high index scores (green). Poor overall water quality is characterized by having low index scores (orange and red).

Chesapeake Bay - Indicator Details:





  Indicator Selection Diagram


Index Map

This map shows the Water Quality Index scores for 2009. Poor overall water quality is indicated by low index scores, and is shown by shades of orange and red on the map. Most regions of the Bay had a Water Quality Index score in the poor to moderate range (20-60%); this is consistent with spatial patterns in recent years. The highest index scores occurred in the James River, Upper Bay, and Lower Eastern Shore (Tangier) regions. Areas of the Potomac River and Mid Bay also had moderate-good water quality. High index scores in these regions are largely attributed to the dissolved oxygen and chlorophyll a levels. The lowest index score occurred in the Patapsco and Back River region.


Creating this map
This map shows the Water Quality Index values for the current year. At each of the 144 monitoring station, the percent (%) frequency that each water quality parameter meets the threshold levels was calculated to provide the Water Quality Index score. Water quality index scores between stations was then estimated by interpolation to visualize spatial patterns and trends.

Ranking


Comparison of Bay Health Index scores for 2009 () compared to
()


Score Legend
 Score (%)
 0               20               40               60               80              100
  
James River  
Upper Bay  
Lower Eastern Shore (Tangier)  
Rappahannock River  
Mid Bay  
Choptank River  
Potomac River  
Overall Bay  
Upper Eastern Shore  
Upper Western Shore  
Lower Bay  
Patuxent River  
York River  
Lower Western Shore (MD)  
Elizabeth River  
Patapsco and Back Rivers  

This figure ranks each region from best to worst Water Quality Index (WQI) score for 2009. The highest ranked regions in 2009 were the James River, Upper Bay, and Lower Eastern Shore (Tangier), all with scores of 52%. The Patapsco and Back Rivers region was the lowest ranked in 2009 with a very poor score of 15%, a decrease from 20% in 2008. Poor Water Quality Index scores (20 to 40%) occurred in the Patuxent, Elizabeth, York, Patapsco and Back rivers, the Lower Western Shore (MD), and the Lower Bay regions.



Excel Spreadsheet