Overall Health Index

The Chesapeake Bay report card compares 10 indicators (dissolved oxygen, nitrogen, phosphorus, chlorophyll a, water clarity, aquatic grasses, benthic community, stewardship, walkability, heat vulnerability index) to scientifically derived thresholds or goals. These indicators are combined into an Overall Health Index, which is presented as a subregion percent score. Other indicators (blue crab, bay anchovy, striped bass, turbidity, protected lands, social index) presented on these pages are not included in the score.

Dissolved Oxygen

The oxygen dissolved in water is critical to the survival of fish and shellfish living in it. All of the living creatures in the water need oxygen to survive but as dissolved oxygen levels decrease, it becomes harder for animals to get the oxygen they need to survive. Low concentrations of dissolved oxygen is often the result of eutrophication, which occurs when there are too many nutrients (such as nitrogen and phosphorus) in the water which cause dense algal blooms to grow. When the algae die and decompose, the decomposition process uses up dissolved oxygen in the water, reducing the oxygen available for fish, and other organisms, which may become stressed or even die.


Nitrogen is important to all living things. Nutrients such as nitrogen occur naturally in both freshwater and saltwater. Plants and animals need nutrients to grow and survive. But when too much nitrogen enters the water it can fuel the growth of algae, creating dense blooms that block sunlight and reduce oxygen for fish and other organisms. Nitrogen runs off the land during rain events. Atmospheric nitrogen from industry settles on the water.


Total phosphorus is an indicator of too much phosphorus in the water. Phosphorus attaches to sediment particles, so phosphorus and sediment pollution are linked. Phosphorus is an essential nutrient for all plants and animals. But too much phosphorus in the water causes algae to grow in large, dense algal blooms, which depletes oxygen for fish and other marine organisms.

Chlorophyll a

Chlorophyll a is the green pigment in tiny marine algae (phytoplankton) that produces food. Measuring chlorophyll is based on the amount of phytoplankton (microalgae), which uses both nitrogen and phosphorus to grow. Too much algae in the water reduces water clarity, and decomposing algae leads to reduced dissolved oxygen. In a balanced ecosystem, phytoplankton provide food for fish, crabs, oysters, and worms. When too many nutrients are available, phytoplankton may grow out of control and form algal blooms that can harm fish, shellfish, mammals, birds, and even people.

Water Clarity

Water clarity is a measure of how much light penetrates though the water column. Water clarity is dependent upon the amount of particles (e.g. suspended sediment and plankton) and colored organic matter present. Clear water is especially critical for seagrasses since, like all plants, they need to be able to absorb the sun’s rays to grow. Excess sediment in the water reduces water clarity by blocking sunlight to seagrasses. Fish and other organisms in the water need aquatic grass habitat to thrive.

Aquatic Grasses

Aquatic grasses provide critical habitat to key species and can improve water clarity. Seagrasses are submerged plants found in shallow waters and are a critical part of the water that provide a number of benefits like buffering coastal communities from storms, removing pollution from the water, and providing shelter for animals.

Benthic Community

Chesapeake Bay

The Benthic Index of Biotic Integrity (BIBI) measures the condition of the benthic community (e.g. clams and others) living in or on the soft bottom areas of the Bay. These organisms are a key food source for many species including perch, spot, and croaker.

Chesapeake Watershed

Stream benthic community measures the condition of the benthic community living in streams. Benthic macroinvertebrates are freshwater organisms including snails, mussels, worms, and insects that live in and on the stream and river bottom. These organisms are a key food source for many fish species.

Blue Crab

Blue crabs are an important living resource in the Bay. They are both predator and prey in the Bay's food web. They use aquatic grasses habitat to hide from predators and to mate and molt. Fishing for blue crabs in the Bay is a recreational and commercial past time.

Bay Anchovy

Bay anchovy is an important living resource in the Bay because it is one of the most abundant schooling fishes in the Bay. It is an important food source for top predators and eats zooplankton (tiny animals floating in the water column). Most bay anchovy do not migrate out of the Bay, but instead spend their whole life here.

Striped Bass

Striped bass, or rockfish, is a key top predator, and uses the Bay as an important spawning and nursery area. Striped bass is Maryland’s state fish and a popular commercial and recreational fishery.

Protected Lands

Conserving land is critical for the health of the watershed and is part of the Chesapeake Bay Program’s Watershed Agreement. This Agreement, signed in 2014, strives to preserve 2 million acres by 2025. The goal is to conserve landscapes to maintain water quality and habitat; sustain forests, farms, and maritime communities; and conserve lands of cultural, indigenous, and community value. The protected lands indicator examines all valuable lands (which includes land to conserve for farms, forests, wildlife habitat, and cultural and natural heritage) and compares them to the land protected with the Chesapeake Conservation Partnership goal to protect 30% of the land by 2030. The data used was from 2018.

More information about this indicator is at Chesapeake Progress.


Turbidity is a measure of water clarity that expresses how much light passes through the water column. It is dependent upon the amount of suspended particles (e.g., sediment, algae, bacteria) and colored organic matter present. Clear water is critical for the growth and survival of fish, crabs, and other aquatic organisms.


Approximately 18 million people live in the Chesapeake Bay Watershed and more are moving in each year. Every day, those 18 million people make decisions that affect the Bay’s health. Without the active participation of these residents, our restoration efforts will be unsuccessful. Individual stewardship is vitally important to the health of local watersheds and the Bay as a whole.

So, how active and engaged are the residents of the Bay watershed? The Stewardship Index was created in 2017 to measure just that. It is the first comprehensive survey of residential stewardship actions and attitudes in the Chesapeake Bay watershed, and one of the first like it in the country. The data presents a powerful resource for agencies and organizations working to foster stewardship, whether it is informing programs that seek to increase the adoption of individual actions, spurring volunteerism and collective action, or cultivating leaders who mobilize others.

Generated from a random probability sample of 5,212 Chesapeake Bay watershed residents, conducted by telephone, the survey measured the following: 19 individual stewardship behaviors and the likelihood of those surveyed to perform those behaviors in the future, levels of volunteerism and civic engagement, and attitudes that impact personal stewardship. The stewardship index will be conducted again in 2022 to measure progress. Meanwhile, the data from the first survey has been used to create a baseline and tools for use in advancing stewardship throughout the watershed.

While you can access the raw data and more background about the Stewardship Indicator on Chesapeake Progress, you will soon be able to explore and manipulate the data through an interactive website, available through the Chesapeake Progress site. This website will allow users to filter the data to identify the best opportunities for behavior adoption, and will provide resources to create an effective behavior change campaign. This website will be available by fall 2021.

Social Index

The Social Index uses data about social vulnerability from the Center for Disease Control and Prevention (CDC) collected within the American Community Survey. Social vulnerability is defined by the CDC as a measure of how able a community is to respond and bounce back from hazardous events such as natural disaster, tornado, or disease outbreak. Some of the measures in the index include socioeconomic status, household composition, diversity, minority status, language, housing, and transportation.


Walkability measures how many people can walk to a park within ten minutes throughout the Chesapeake Bay Watershed. This idea was developed by the Trust for Public Land. Access to parks within a ten-minute walk provides space for people to gather with friends, exercise, and maintain mental health in a safe outdoor environment. Often, communities of color and underrepresented communities do not have the same access as other groups.

Heat Vulnerability Index

A Heat Vulnerability Index, developed by NASA and Groundwork USA, is a watershed indicator in the report card. This index includes four metrics: tree canopy, impervious surface, land surface temperature, and households in poverty. The index identifies places where there is greater vulnerability of people to heat-related and flooding-related risks, which are often in neighborhoods with race-based housing discrimination. Other groups at risk are communities of color, low-income communities, children, and the elderly. This index can help managers prioritize locations for restoration projects such as tree plantings and conversion of abandoned impervious surfaces to green space.