About half of the U.S. population lives along the coast. All of these people create a demand for homes, roads, and other infrastructure. If current rates of coastal development continue, more than one-quarter of the nation’s coastal lands will be altered by 2025.

Past development affects habitat as well. More than 75,000 large dams and more than 2.5 million total barriers block fish from reaching 600,000 miles of rivers and streams in the United States. Many of these dams are decades old and no longer in use or in disrepair, but they still affect fish migration.

More than 60 percent of our coastal rivers and bays are moderately to severely degraded by nutrient runoff. Excess nutrients reduce water quality and lower the level of oxygen in the water. They can also cause algal blooms and “dead zones,” making it difficult for fish to survive.

Pollution doesn’t just affect fish—it can affect corals, too. When excess sediment and nutrients flow from the land into the ocean, they can smother coral reefs. This reduces the light and food that can reach the reefs and can damage or kill them.

Climate change will have a wide range of effects on habitat. The increased temperatures will lead to sea level rise and increased extreme weather events. In the United States, a sea level rise of 1 foot could eliminate 17 to 43 percent of today’s wetlands.

Ocean acidification, a result of the ocean absorbing increased carbon dioxide, makes it harder for coral reefs to grow. Warmer ocean temperatures increase the number of coral bleaching events. Corals can survive bleaching events, but they often die if the stressful conditions continue for an extended period.

Extreme weather events will lead to coastal habitat loss. Hurricanes and other storms destroy wetlands and other coastal habitats through erosion and flooding, and waves can damage coral reefs. This loss leaves coastal communities more vulnerable to future storms. Droughts and heat waves alter habitat conditions and affect the migratory patterns of fish and other wildlife.

Over the past century, habitat loss has been the most common cause of extinction for freshwater fish in the United States. Many saltwater fish are also in decline due to habitat degradation. When habitats are damaged or lost, they are difficult and costly to restore.

Since the early 1600s, the United States has lost more than half of its wetlands (more than 110 million acres). Coastal wetlands continue to disappear at higher rates than those further inland. The coastal watersheds of the continental United States lost wetlands at an average rate of 80,000 acres a year from 2004 to 2009.

In addition, fish nursery grounds are significantly affected by the loss of seagrass habitat. Recent trends indicate seagrass habitat losses of 50 percent in Tampa Bay, 76 percent in the Mississippi Sound, and 90 percent in Galveston Bay. Seagrass beds in the Chesapeake Bay declined 46 percent from 2008 to 2012.