Chesapeake Bay - Indicator Details:

This map shows how often chlorophyll a concentrations were above or below threshold concentrations between March and September 2009. Good water quality is characterized by chlorophyll a levels that are frequently below the threshold, resulting in high scores (shown in green). Poor water quality has chlorophyll a levels that are frequently above the threshold, resulting in low scores (shown in shades of orange and red). In 2009, a large portion of Chesapeake Bay had chlorophyll a levels that frequently exceeded threshold levels. These low scoring regions include most of the mid and lower mainstem Bay, the Lower Western Shore (MD), the York River, and the Patapsco and Back Rivers. Regions of Chesapeake Bay with chlorophyll a concentrations frequently below threshold levels (i.e., in good condition) tended to be in the upper reaches of the tributaries and Upper Bay region.

This map shows average chlorophyll a concentrations in Chesapeake Bay from March to September 2009. Highest average chlorophyll a concentrations tended to occur in the Patapsco and Back Rivers, as well as portions of the Lower Western Shore (MD), Upper Eastern Shore, and the James River reporting regions. In these areas, average chlorophyll a concentrations often exceeded 25mg/l; these high concentrations are more than likely due to elevated nutrient availability. Low average chlorophyll a concentrations (in the 5-10 mg/l range) occurred in many areas of the bay this year, including most of the Mid and Lower Bay, Lower Eastern Shore (Tangier), and the upper reaches of the Potomac and York Rivers.