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Browse History: Water Quality Index (2007)
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:





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Index Map

This map shows the Water Quality Index scores for 2007. Poor overall water quality is characterized by having low index scores, which 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%). Highest index scores occurred in the Elk River and the Upper Bay and Upper Western Shore regions. Areas of the James and Potomac Rivers also had moderate-good water quality. High index scores in these regions are largely attributed to the dissolved oxygen and chlorophyll a levels. Lowest index scores occurred in the Patapsco and Back Rivers and the Lower Western Shore (MD) tributaries.

Creating this map
This map shows the Water Quality Index values for 2007. 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 using spatial interpolation software.

Ranking


Comparison of Bay Health Index scores for 2007 () compared to
()


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

This figure ranks each region from best to worst for the Water Quality Index (WQI) for 2007. The best water quality rating in 2007 was moderate (40-60%), recorded in the Upper Western Shore, Upper Bay, James, and Choptank River regions. Many regions had a poor Water Quality Index score in 2007, with the Lower Western Shore (MD) and the Patapsco and Back Rivers having the lowest score.


Excel Spreadsheet