About the Indicators

The health of the Chesapeake relies on intricate natural systems that filter water and provide habitat for diverse and abundant life. CBF scientists measure its health by examining the best available historical and current information for 13 indicators in three categories: pollution, habitat, and fisheries. Taken together, these indicators offer an assessment of the Chesapeake's health.


  • Nitrogen & Phosphorus

    Excess nitrogen and phosphorus are the Bay's two primary pollutants, fueling algal blooms that cloud the water and use up life-sustaining oxygen when they die and decompose, causing the Bay's dead zone. The primary sources of nitrogen and phosphorus pollution are agricultural, urban, and suburban runoff; sewage treatment facilities; and air deposition. These pollution loads are largely driven by river flows and precipitation. Rain and snowmelt wash these and other contaminants off farmland, lawns, and city streets into local streams, rivers, and ultimately the Bay. However, protecting and restoring habitats like forested buffers and wetlands, and implementation of practices such as rain gardens and cover crops will help make the Bay less susceptible to the vagaries of weather by reducing the flow of water and associated pollution from the land. Find out more about the impact of nitrogen and phosphorus.

  • Dissolved Oxygen

    The volume of the Bay and its tidal rivers with little or no dissolved oxygen is called the "dead zone." Nitrogen and phosphorus pollution fuel enormous algal blooms that eventually die, sink to the bottom, and are decomposed by bacteria, which use up oxygen in the process, resulting in oxygen-deprived waters unable to support aquatic life. In a typical year, the amount of nitrogen and phosphorus pollution that flows into the Bay during the spring largely influences the size of the summer dead zone. Reducing pollution to improve this indicator—and the Bay's capacity to support aquatic life—remains the main challenge of Bay restoration. Find out more about dissolved oxygen.

  • Water Clarity

    Water clarity is measured as the depth in the water column to which sunlight is able to penetrate. Sunlight is vital to the growth and reproduction of underwater grasses. Underwater grasses are critical to the Bay ecosystem as they trap sediment, provide habitat for fish and crabs, and food for waterfowl. Water becomes cloudy in the presence of excess sediment, algae, and other particles suspended in the water column. Loss of riparian buffers and wetlands, as well as poor agricultural practices that accelerate soil loss, increase the amount of sediment that flows into streams, rivers, and the Bay. Like dissolved oxygen above, water clarity is also negatively affected by the phosphorus and nitrogen pollution that fuels dense algal blooms, which cloud the water and block sunlight.

  • Toxics

    Toxic chemicals from air deposition, urban runoff, and hazardous waste sitescontinue to degrade the health of the Bay and its tributaries. Over 70 percent of the Bay and its tidal rivers remain impaired due to chemical contaminants. Improvement is slow due to the persistent nature of many chemicals, especially PCBs and mercury, which cause most of the region's fish consumption advisories. Also of concern is the limited knowledge we have about the potential effects of personal care products and pharmaceuticals released from wastewater treatment plants, septic systems, combined sewer outflows, and animal agriculture. Find out more about chemical contamination in Chesapeake Bay waterways.


  • Forested Buffers

    Planting trees is one of the best things we can do for our environment. In addition to serving as filters that trap nutrient and sediment pollution, forested buffers also provide habitat for wildlife, help reduce greenhouse gases by sequestering carbon, and can reduce air pollution. The states' Cleanwater Blueprints are relying heavily on this practice to help restore local rivers, streams, and the Bay. To accelerate progress, we must develop new incentives and approaches for encouraging protection and restoration of these critical pollution filters. Find out more about the important role of trees and forested buffers.

  • Wetlands

    Water-saturated lands like marshes or swamps—commonly known as wetlands—are a vital link to Bay health. They provide valuable habitat and act as natural filters that improve water quality by trapping and treating polluted runoff. For example, marshes in the tidal Patuxent River in Maryland are estimated to remove about 46 percent and 74 percent of the total nitrogen and phosphorus inputs, respectively. Wetlands can also help mitigate sea level rise and provide natural protection from storm surges.

    Even though wetlands act as the Bay watershed's kidneys to absorb and cleanse polluting runoff, protecting them and increasing their acreage continues to be a struggle. Meanwhile, wetland losses due to sea level rise and illegal and unregulated activities degrade the health and functioning of existing wetlands. We must accelerate all efforts to increase the over-all health of these natural water treatment systems in the watershed.

  • Underwater Grasses

    Underwater grasses are an essential component of the Chesapeake Bay ecosystem. They provide crucial habitat and nursery grounds for fish and crabs and provide food for waterfowl. They also remove pollutants from the water and help reduce shoreline erosion by softening wave action. Grasses are a good indicator of the state of the Bay because their health and abundance is very closely linked to water quality. Find out more about the role of underwater grasses.

  • Resource Lands

    The conservation of resource lands—filtering forests and open spaces and working farmland—is crucial to limiting pollution to local rivers, streams, and the Bay. Land conservation funding, effective state and local growth management policies, and prevention of sprawl-type growth are critical to maintaining the health of our waterways. Find out more about the connection between resource lands and the Bay.


  • Rockfish (Striped Bass)

    Rockfish spend the first three to eight years of their life year-round in the Bay before migrating up the East Coast. The survival of the rockfish population is dependent upon both the health of the Bay and regulation of the fishery. Physiological stresses that can increase rockfish mortality include low dissolved oxygen levels, habitat problems, and poor nutrition due to the limited availability of their preferred prey, menhaden. Find out more about the challenges facing the Chesapeake's rockfish population.

  • Oysters

    Low oxygen levels driven by intense algal blooms, sediment runoff, availability of substrate for rebuilding oyster reefs, and poaching on closed bars all impact oyster populations. Sediment coats reef substrate, preventing attachment by oyster larvae. Low dissolved oxygen levels reduce oysters' resistance to disease. The biggest challenge is lack of reef habitat. Oyster shells, the preferred natural substrate, are limited in quantities, so scientists are trying alternative materials. Find out more about the challenges facing the Chesapeake's oysters.

  • Blue Crabs

    Loss of underwater grass beds—a critical protective habitat for juvenile crabs—and low dissolved oxygen has reduced the number of crabs that can be produced and maintained by the Bay. As a result, the crab population cannot sustain high levels of harvest by crabbers. Fishery management can hold the catch at sustainable levels, but restoration of a healthy crab population and a productive fishery will also depend on improved water quality and habitat. Find out more about the challenges facing the Chesapeake's blue crab population.

  • Shad

    Once the most valuable fishery in the Chesapeake, shad are now in danger of being the forgotten fishery and will only recover with a formula that includes restocking of juveniles, protecting adult fish in the ocean and the Bay, and restoring access to historic spawning grounds. Find out more about the challenges facing the Chesapeake's shad fishery.

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