Threats to Estuaries

Population Growth in Coastal Watersheds

Coastal counties account for only 11% of the nation’s (lower 48) land area, but nearly 50% of the entire population lives in these coastal areas. It has been difficult to control and manage the increased growth that has resulted from this population increase. Inadequate protective environmental safeguards have led to the elimination of millions of acres of habitat.

For example, in Maryland, 10 years ago every new person added to the state accounted for the loss of 1/3 acre of land; now, every new person causes the loss of 2/3 acre — from housing developments, shopping malls, business parks, and new roads. Without effective safeguards for streams and estuary shorelines, the enormous numbers of people who will continue to settle near estuaries may well end up loving them to death.

Dredging, Draining, Bulldozing, and Paving

Thousands of acres of estuary habitat, including salt marshes, seagrass meadows, beaches, and shellfish beds, are altered or completely destroyed every year by countless activities that do not meet environmental safeguards. Dredging, draining, bulldozing, and paving are a few of these activities.

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. More information »

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 factors towards 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. More information »

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 caused one of the most catastrophic human-caused natural 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. Human activities that result in oil spills or other devastating events endanger every aspect of estuarine habitats, and it will continue to be this way unless people take action.

Polluted Runoff from Rural, Suburban, and Urban Areas

Storm water picks up a multitude of contaminants from roads, vehicles, lawns, and construction sites and dumps it in the nearest stream. Contaminants and chemicals from land drain into the estuary, polluting the bay and degrading the habitat. When habitat along stream channels is destroyed by poor agriculture or forestry activities or by building too close to the stream, fish die because their nesting and feeding areas are destroyed. In urban harbors especially, polluted runoff into the estuary creates “hot spots” of toxic contamination where nothing can live. An annual “dead zone,” or area of water with dangerously low oxygen content, extends more than 7,000 square miles into the Gulf of Mexico off Texas and Louisiana due to polluted runoff from agricultural chemicals. Airborne pollution that falls on estuaries also contributes to these problems.

Perhaps one of the biggest consequences of pollution and contaminants in estuaries is eutrophication. Eutrophication is 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. This often happens as a result of decreased oxygen levels caused by pollutants in the watershed. Agriculture, wastewater treatment plants, urban runoff, and consumption of fossil fuels all contribute to this process. These algal blooms are problematic because they can last for months at a time, blocking essential sunlight for submerged aquatic vegetation and causing them to die off. Eutrophic symptoms in coastal waters can also pose an enormous threat to human health, caused by the consumption of fish and shellfish contaminated by the toxins found in algal blooms.


Hydroelectric and flood control dams block upstream and downstream passage for migrating fish, isolating them from vital spawning and feeding areas. 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. Without healthy streams, estuaries do not receive their natural allocation of nutrients. The result is an overall reduction in the productivity of estuary waters. 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.

Sewage Discharges

City and industry sewage treatment plants that do not have advanced technology dump far too many nutrients and pathogens in the water to sustain an environment fit for living organisms. Fish, humans and the native living organisms of a healthy estuary ecosystem require clean water to survive and thrive. When the treatment plants discharging into Tampa Bay were upgraded to advanced technology, the sea grasses, 85% of which had been destroyed, began to grow back, and along with them the fish and other creatures that depend on them. Across the country, water quality standards are regularly violated. A recent EPA report noted that nearly 40% of the nation’s rivers, lakes, and estuaries are too polluted for safe fishing and swimming.

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.

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