National Estuaries Week!

Thank you to Restore America's Estuary for this amazing information, images and educational video! We hope you enjoy it as much as we do!

What is an estuary?

An estuary is a partially enclosed body of water formed by fresh water from rivers flowing into and mixing with ocean saltwater. The fresh water is often prevented from flowing into the open ocean by land masses such as peninsulas, islands, or surrounding salt marshes. This makes estuaries unique environments that sustain a diverse biological community of plants and animals. Some of the most commonly known estuaries in the United States are the Chesapeake Bay, Puget Sound, and the Indian River Lagoon.

Estuary Zones

Supratidal Zone Intertidal Zone Subtidal Zone
Area above high tide that extends into higher lands. This is also known as the splash zone or supralittoral zone. Area that is covered during high tide and barren during low tide. Often includes rocky cliffs and mud flats. There are very few organisms that are resilient enough to live in this harsh environment. Also known as the littoral or transition zone. Area that extends past the low tide line into open waters. This area is continuously covered by water.
Organisms: Algae, fungi, snails, barnacles Organisms: Crabs, barnacles, mussels, shrimps, snails, sea urchins Organisms: Fish, marine organisms, crabs

Diagram courtesy of Project Watershed.

Coastal Habitats

Coastal habitats can vary depending on geographic region. The three main types of estuary habitats include salt marshes, seagrass, and mangroves. RAE works to restore all of these habitats in order to preserve an ecosystem that has brought tranquility, education, and jobs to millions of people all over the country.

Salt marshes are coastal wetlands dominated by grass and shrub plants. Salt marshes are often characterized by having very high salinity (salt content) and sporadic small islands. Organisms that live here must withstand harsh environments due to rapidly changing tides and salinity. In addition to providing key marine habitat, salt marshes help to filter pollutants, stabilize the shoreline, serve as a buffer to storms and flooding, and sequester and store large amounts of carbon.

Seagrass (or submerged aquatic vegetation) habitats are constantly submerged underwater and consist of aquatic grasses, providing food and shelter to many aquatic species. These species include, but are not limited to, fish, crabs, manatees, and sea turtles. Sea grasses are very sensitive to water pollution and changes in pH.

Mangroves are a type of tropical forest found in coastal areas that are regularly flooded by tidal water. They are among the most carbon-rich forests in the tropics and provide many ecosystem services. They provide spawning grounds for fish species, filter pollutants from coastal waters, and protect coastal development and communities against storms, floods, and erosion. These unique evergreen plants can withstand high salinity and harsh environments.

Salt marsh

Sea grass


Why are estuaries important?

Maintains Vital Food Supplies
Healthy estuaries produce more food per acre than the richest Midwestern farmland because of the fertile mix of nutrients from land and sea. Because of this, there are many types of species that are harvested for human consumption, such as Chesapeake Bay blue crab.

Protect Nature's Bounty
Beyond providing food for our consumption, estuaries are the home of thousands of species of fish, birds, plants, and animals that depend on healthy habitat for their survival.

Supports the Economy
There are 56 million jobs in the fishing, tourism, and recreational boating industries — all of which depend on healthy estuaries for their products and customers. Estuaries and coastal waters provide essential habitat for 75% of America's commercial fish catch and 80–90% of the recreational fish catch. In addition, estuaries provide significant "services" which directly benefit Americans. For example, estuaries protect landowners from flood waters and provide important buffers that protect water quality by filtering runoff.

Preserves a Way of Life
Healthy estuaries support unique, centuries-old cultures, traditions, and ways of life dependent upon the diversity of wildlife for everything from livelihoods to storytelling. Estuary restorations will maintain these ways of life — and the heritage they embody — for the benefit of future generations.

In addition, nearly 200 million Americans — approximately 70% of the population — visit estuaries and coastal areas every year for vacations, recreation, sport, or sightseeing. The more we do to restore estuaries, the more Americans will be able to experience their amazing bounty.

For the 110 million Americans who live near estuaries, they are essential to people's quality of life: for their scenic beauty, for their recreational opportunities, for their bounty, for their abundance of life, and for their mere presence. Restoring estuary habitat is the only way to ensure that this quality of life is protected and improved.

Provides Ecosystem Services
Estuaries also act as storm buffers to the mainland, protecting residential areas from harsh storms such as hurricanes. When flooding occurs, estuaries soak up a lot of the excess water and lessen the damage dealt to local habitats and communities.

Estuaries also naturally remove pollutants like toxic chemicals, excess sediment, and excess nutrients. Organisms like salt marsh plants and oysters act as filters, clearing the water and making it safer for other living things.

In addition, coastal wetlands also remove and store large amounts of carbon — an ecosystem service referred to as blue carbon.

Estuaries are an educational resource that must be maintained as living laboratories of life. As one of the most biologically diverse ecosystems in America, the opportunities for learning are endless. In order to secure these educational opportunities for future generations, restoring and protecting estuaries is essential.

Climate Change & Estuaries


Water in the streets during a high tide event on a storm-free day in Baltimore, MD. Courtesy of NOAA.

Sea level rise: Estuaries are under constant danger of rising sea levels. Sea level rise is often broken into two categories: global and local. Global sea level rise is the increase in the ocean’s average height across the world. Local sea level rise is an increase in the height of the water relative to a specific place on land. Climate change has caused global sea level to rise through a combination of thermal expansion (water expanding as it warms) and the increased melting of land-based ice (such as glaciers). Factors like land subsidence, gravitational forces, and ocean currents can impact the rate of local sea level rise, often resulting in a higher rate when compared to the global average. Many coastal cities are already experiencing the effects of sea level rise, such as flooding and intensified storm surges.

This increase in water levels can severely damage estuaries and wetlands. Plants meant to live above the water line are now being drowned and there is ever-decreasing light availability to submerged aquatic vegetation. Sea level rise also increases the amount of flooding and erosion in coastal areas. If this trend continues, the erosion of beaches will become very severe, destroying dunes that are essential to the prevention of landslides and slumping (when rock and other matter moves a short distance down a slope). Sea level rise can also push native species from the area in search of healthier habitats, allowing invasive species to dominate. 

Saltwater intrusion is the movement of saltwater into freshwater aquifers, which extend beyond the boundaries of an estuary. Excessive groundwater pumping and sea level rise are the main causes of this intrusion. As water levels rise, saltwater stretches further inland, increasing the salinity of water that was once fresh. With less freshwater flowing downstream toward the estuary, the saltwater easily extends beyond the zone of transition (where freshwater and saltwater mix). This can put stress on plants and animals and may even cause the disappearance of certain species when the salinity level reaches above their tolerance.

Changing rainfall patterns also create problems for estuaries. An increase in rain results in more runoff, sedimentation, and erosion, threatening the ecosystems of estuaries. On the other hand, decreased precipitation can raise the salinity of estuaries by reducing the incoming freshwater.

Bleached coral at Lisianski Island in Papahanaumokuakea Marine National Monument. Courtesy of NOAA.

Ocean acidification is currently affecting the entire world’s oceans, including coastal estuaries and waterways. Acidification happens when carbon dioxide in the air is absorbed by the saltwater, turning the water acidic as a result. This causes harm to organisms made from calcium carbonates (like coral) because calcium carbonates dissolve in acidic substances.

For example, coral “bleaching” is caused in part by ocean acidification. When coral are exposed to stressors like acidic oceans, warmer water temperature, or pollution, they expel the algae that live in their tissue. This leaves them completely white, or “bleached.” The bleached coral can recover, but with no source of energy they have an increased vulnerability to disease and death. Healthy coral reefs absorb 97% of a wave’s energy, which buffers shorelines from currents, waves, and storms, helping to prevent loss of life and property damage. Coastlines protected by coral reefs are also more stable in terms of erosion than those without

Eutrophication, a process where excess nutrients in the water lead to the growth of algae on the surface of the water, worsens with climate change. Warm water with high carbon dioxide content provides ideal conditions for algal blooms, while increased nutrient runoff from altered rainfall patterns feeds the algae. Eutrophication is a problem for estuaries because it decreases the light and oxygen for other species.

Algal blooms at the Assateague Island National Seashore, MD. Courtesy of the EPA.

Restore America’s Estuaries Position on Climate Change

Coastal habitats are being subjected to a range of stresses from climate change and many of these stresses are predicted to increase over the next century. The most significant effects are likely to be from sea-level rise, increased storm and wave intensity, temperature increases, ocean acidification, and changes in precipitation that will alter freshwater delivery. These climate change forces are having dramatic effects on coastal habitats and the species dependent on these ecosystems. Addressing the challenges posed by climate change will require a combination of adaptation and mitigation to the changes that are likely to occur and global reductions of greenhouse gas (GHG) emissions from anthropogenic sources. Most importantly, overcoming these challenges will require dissimilar groups and interests being able to have open, and sometimes difficult, conversations that lead to action.

Read our full statement here.


Sites Referenced:

Threats to Estuaries

Population Growth in Coastal Watersheds

Coastal counties in the United States directly situated on the shoreline account for less than 10% of land (excluding Alaska). However, in 2010, 39% of the nation’s population resided in these coastal counties. This is an increase of 40% since 1970, and the number is only expected to increase in coming years. It has been difficult to control and manage the increased growth that has resulted from this population boom. Inadequate environmental safeguards have led to the elimination of millions of acres of habitat, including vital estuaries and wetlands.

Dredging, Draining, Bulldozing, and Paving

Thousands of acres of estuary habitat, including salt marshes, seagrass meadows, and mangroves, are altered or destroyed every year. Some of the activities that cause this destruction include dredging, draining, bulldozing, and paving.

Dredging. Courtesy of NOAA.

Dredging is the removal of sediment and other natural materials from the bottoms of bodies of water, such as lakes and rivers, in order to create open waterways for the passage of boats and ships. This process prevents the natural buildup of sediment in channels and harbors and causes sediment particles to flow into an estuary, making the waters murky and unhealthy. Other effects include a reduced amount of nutrients flowing from marshes, an alteration in tidal patterns, and the contamination of water, making the environment unsuitable for plant and animal life. Though dredging is essential to the process of waterway transportation, its effects are detrimental to coastal estuarine habitats.

While dredging to remove sediment can have negative impacts, accelerated sedimentation as a result of human-caused erosion is also an issue. Humans can increase the rate of erosion through practices like deforestation and agriculture. This can lead to an increased rate of sedimentation that smothers marine life and upsets the balance of estuaries.

Up until a few decades ago, estuaries were often drained and filled in to create new spaces for agriculture, shipping ports, or urban areas. The destruction of these estuaries caused a major loss to coastal environmental health.

Bulldozing and paving over estuarine waterways is proving to be one of the most destructive activities for these ecosystems. With our growing population, coastal areas have become a hotspot for residential areas. In order to accommodate these population increases, estuaries and waterways are being paved over, causing massive ecosystem damage.

Oil and Gas Drilling

The drilling for oil and gas, especially in the Gulf of Mexico, is becoming an increasingly concerning problem for our nation’s estuaries. The BP oil spill in 2010 was one of the most catastrophic human-caused disasters in history. According to the National Wildlife Federation, as many as 8,000 birds, sea turtles, mammals, and other species were found injured or dead in the first six months of the oil spill. Nearly a decade later, oil from this spill is still causing detrimental effects to the salt marshes of the Gulf Coast. While there has been some progress, the more heavily impacted salt marshes will still take many years to recover. Previous oil spills have even affected the invertebrates, like (example), of salt marshes for over 4 decades.

Nutrient Pollution

A close look at algae blooms. Courtesy of EPA.

Storm water runoff carries a multitude of contaminants, including phosphates and nitrates, from sewage, animal waste, and fertilizers into nearby streams. These contaminants and chemicals drain into the estuary, polluting bays and degrading habitats. In urban harbors especially, polluted runoff into the estuary creates “hot spots” of toxic contamination where nothing can survive.

Excess nutrients can lead to eutrophication, a phenomenon caused by excess nutrients in water systems resulting in massive algal blooms, or the growth of large amounts of algae that cover the water’s surface. As algae die, the process of decomposition depletes oxygen levels within the water. The water can become low in oxygen (hypoxic), or completely depleted of oxygen (anoxic). These hypoxic and anoxic areas are often known as “dead zones,” because organisms either die or are forced to leave the area. As of June 2017, the world’s biggest dead zone is in the Gulf of Mexico. Measuring roughly 8,776 square miles, this dead zone is approximately the size of New Jersey.

Eutrophication can pose additional problems, as well. The massive algae blooms can last for months at a time and block light from other organisms beneath the surface, making it even harder for living things to survive. Additionally, some algae blooms are toxic, posing a risk to both the organisms in the estuary and any humans who may consume shellfish or come into contact with the algae.

Industrial Pollution

Industrial pollution is another threat facing estuaries. Toxic substances, including chemicals and heavy metals, can enter estuaries through industrial discharges and stormwater runoff. Many of these substances are poisonous, carcinogenic (cancer-causing), or otherwise dangerous. As they are consumed by plants and animals, they accumulate in the tissues of living things. As the toxins travel up the food chain, they become more harmful for organisms at the top of the food chain, including humans. These toxins cause stress on the ecosystem, lowering its resilience and productivity.


Oysters. Courtesy of NOAA.

Overharvesting refers to catching a species, like fish, oysters or crabs, faster than they can naturally replenish. Removing any one species can alter the entire ecosystem and have devastating effects. For example, the oyster population of the Chesapeake Bay was nearly wiped out due to overharvesting. Because oysters serve as water filters within the Bay, many other organisms were also put at risk as harmful pollutants remained in the water.

Through the management of oyster harvests and the establishment of sanctuaries, the Chesapeake Bay’s oyster populations are on the road to recovery. This progress is vital for the health of the Bay, since NOAA has found that the areas with higher oyster densities have clearer and healthier water. Additionally, oyster reefs can bring millions of dollars into local economies through ecosystem services.

Reduced Freshwater Inflows

A freshwater inflow is the water that flows from streams and rivers into estuaries, mixing with the marine waters. Estuaries cannot function without these freshwater inflows, as they are needed to maintain their structure and function. However, human activity has resulted in the reduction of these much needed inflows.

Dams, which block the natural routes of streams and rivers, reduce the amount of freshwater that can reach an estuary. The construction of dams for hydroelectric power accounts for significant and ongoing loss of habitat in the watersheds of many of our nation’s estuaries. Freshwater inflow is also being affected as humans extract water upstream and from aquifers to satisfy society’s water needs.

The reduction of freshwater inflows reduces the amount of nutrients that reach the estuary, which some estuarine organisms rely on. Fewer fish returning to the estuary wreaks havoc among the many living organisms in the food web that depend on healthy populations of fish, thus also impacting the fishing industry that many people rely on for food and jobs. Decreased freshwater also causes the salinity of an estuary to increase, making life in the estuary unhealthy for some species.

Invasive Species

Brazilian Peppertree. Courtesy of the US Department of Agriculture.

Invasive species are plants and animals that have been introduced to habitats outside their native ecosystems. Many invasive species are introduced to estuaries through the ballast water of ships; this is the water ships hold to remain balanced. When this happens, organisms can be sucked into the tanks in one area, and redeposited in another, introducing non-native species to new locations.

Invasive species compete with and prey upon native species, reducing their populations and sometimes driving them to extinction. They can reshape entire ecosystems by destroying habitats and altering the relationships between predator and prey, resulting in environmental and economic loss. Invasive species are also known to spread quickly because they have no natural enemies in their new habitats. This means that the problem usually grows worse and worse!

Some examples of invasive species that are problematic for estuaries are purple loosestrife, oyster drills, Chinese mitten crabs, and Brazilian pepper trees.

Coastal Land Loss

Shifts in climate and human manipulation of stream channels cause the loss of tens of thousands of acres of estuary habitat every year. Annually, Louisiana estuaries lose about 25,000 acres to land loss and subsidence (actual sinking of the land into the water). This is also a problem in the Chesapeake Bay.

Climate Change

Information on the impact of climate change on estuaries can be found on our climate change page.

Sites Referenced:

Economics of Estuaries

Estuaries, the transition zones where rivers meet the sea, provide the focal point around which coastal communities grow. The local bay or sound nurtures a high quality of life and maintains the health and traditions of our communities.

An estuary is also a tremendous economic resource which provides jobs to coastal communities. The U.S. coasts generate roughly 56 million jobs.

Many of these jobs come from commercial and recreational fishing, which alone employ 1.7 million people and contribute $212 billion to the nation’s economy. And it’s important to keep in mind that:

The Tijuana River National Estuarine Research Reserve. Courtesy of NOAA.

  • Estuaries produce more food per acre than the most productive mid-western farmland;
  • 75% of commercial fish and 80-90% of recreational fish species depend upon estuaries for their primary habitat, spawning grounds, and nursery areas;
  • Shore adjacent counties account for more than 43% of total United States GDP;
  • Coastal tourism generates an economic value of about $531 billion;
  • Employment for coastal tourism and recreation increased by 6.3% from 2015 to 2016, faster than the overall US economy’s growth of 1.7%.;
  • Estuaries do far more for our economy than supporting industries and providing jobs. Estuaries provide significant “services” which directly benefit Americans. For example, estuaries protect landowners from flood waters and provide important buffers that protect water quality by filtering runoff.

Beyond these measurable benefits, estuaries are at the heart of so many of our coastal communities. Without healthy estuaries, ways of life that have defined our communities for generations would disappear. The value of restoring and strengthening our estuaries can, in the end, really only be measured by the value each of us place on the quality of life we pass on to our future generations.

Additional Resources

Read the report Jobs & Dollars: Big returns from coastal habitat restoration.

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