Everything that happens on the land affects the health of the Chesapeake Bay. Human activities (pollution and land use) and natural factors (rainfall, temperature, and other conditions) have a significant influence on the health of the Bay and its watershed, and continually challenge efforts to protect and restore it.

Determining the health of Chesapeake Bay includes looking at water quality, benthic habitat, and fisheries to determine 'How is the Bay doing?'. The Bay Health Index specifically is determined by averaging seven indicators - total nitrogen, total phosphorus, dissolved oxygen, chlorophyll a, water clarity, aquatic grasses, and benthic community - together into one overarching Index. Each indicator is compared against a goal or threshold and rated on a 0 to 100% scale. Each indicator score is then averaged into an overall Bay Health Index score for each of the 15 reporting regions.

The maps below show the overall health of the Chesapeake Bay (Bay Health Index) or individual indicators by region. Use the slider to look at different years, or click on each indicator for more information.