Water Quality

Just like on land, animals in the water need oxygen to live. Dissolved oxygen is a measure of how much oxygen is available for fish, crabs, clams, shrimp and other life in the Bay. Levels of dissolved oxygen in the water vary throughout the Bay and are affected by many different factors, such as depth, temperature, wind, and time of year. Generally, there is more oxygen near the surface of the water where it meets the air, and less oxygen closer to the bottom. Warmer water also holds less oxygen than colder water.

Water clarity is measured as the depth in the water column to which sunlight is able to penetrate. It is an important part of water quality because sunlight is vital to the growth and reproduction of underwater grasses and other aquatic plants, which form critical habitat for fish and wildlife.

Measures of chlorophyll-a are used to determine how much algae is growing in the water. In excess, these tiny plants can indicate poor water quality because they can lead to both lower dissolved oxygen levels and cloudier water. Certain kinds of algae can also produce toxins that are harmful to wildlife and humans, and blooms of algae can impact uses such as recreation.

Nitrogen and phosphorus are nutrients that occur naturally in the environment, however excessive amounts fuel unnaturally high levels of algae growth in the water. The algae in turn reduce water clarity, blocking sunlight from reaching underwater grasses that serve as food and habitat. When the algae die, they are decomposed by bacteria that consume the oxygen in the water. When too much oxygen is used up, it can result in dead zones where fish and wildlife cannot survive. Excessive amounts of nitrogen and phosphorous come from fertilizers, wastewater, septic tank discharges, air pollution, and runoff from farms, cities, and suburbs.

Too much sediment—tiny particles of dirt, sand, and clay floating in the water—turns the water cloudy, also blocking sunlight from reaching aquatic grasses. Oysters and other bottom-dwelling species can be smothered when that sediment finally settles to the bottom. Excessive amounts of sediment are carried into our waterways from eroding land and from construction sites.

Toxic chemicals from the air, urban runoff, and hazardous waste sites continue to degrade the health of the Bay and its rivers and streams. 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 emerging contaminants from personal care products, microplastics, and pharmaceuticals released from wastewater treatment plants, septic systems, and animal agriculture.

The Chesapeake Bay watershed—the geographical area from which all water ultimately drains into the Bay — spans 64,000 square miles across six states and the District of Columbia. This vast area is a single ecological system, and water quality in one place can significantly influence water quality—and the life it supports—in another. CBF has long advocated for a collaborative, watershed-approach to restoration for this very reason. We helped drive the signing of the first Chesapeake Bay Agreement between Bay states and the federal government in 1983 that established the regional partnership to restore the Bay, including its water quality. We continue to advocate for this unique and critical partnership today.

In 2009, with all voluntary efforts to clean up the Bay over the previous 26 years having failed, CBF and a group of partners filed suit against the U.S. Environmental Protection Agency. We asserted that the agency was legally required to use its authorities under the Clean Water Act to set science-based limits on the amount of pollution entering the Chesapeake Bay in order to remove it from the federal “dirty waters” list.

The settlement of the lawsuit in 2010 resulted in a historic, binding agreement to reduce pollution. EPA set specific limits on the amount of nitrogen, phosphorus, and sediment that can enter the Bay and its tidal rivers, known as the Total Maximum Daily Load (TMDL). In addition to the settlement, the six Bay states and the District of Columbia agreed to develop individual plans and milestones to achieve those limits by 2025, and EPA committed to holding them accountable and imposing consequences for failure if necessary. Together, the limits, plans, milestones, and consequences make up the Chesapeake Clean Water Blueprint.

The Blueprint was adopted as part of the Chesapeake Bay Agreement in 2014. Despite tremendous clean water progress across the watershed, the partnership will not meet the pollution reduction goals by the 2025 deadline. However, state and federal governments are still legally required to meet the targets and sustain them over the long term, and CBF will continue to hold them accountable.

We work throughout the Chesapeake Bay region to restore the natural infrastructure, like oyster reefs and forests, that help reduce pollution and improve water quality in local streams and the Chesapeake Bay. In addition, we advocate at the local, state, and federal levels to advance policies and regulations that improve the health and resiliency of the Chesapeake Bay, its people, and its fisheries—including holistic solutions that target pollution hotspots. We also continue to hold polluters, regulators, and decision-makers accountable for clean water.