Why We Love Estuaries

New York, Tokyo, Seattle, London, San Francisco.

Besides being major international cities, what do these places have in common?

If you guessed that they are all located on estuaries, you are correct!

New York Harbor, photo courtesy NASA

New York Harbor, photo courtesy NASA


These cities were settled when we relied on ships to move people and goods over long distances, and estuaries were very important to shipping. Estuaries form where rivers flow into the sea. Because they are usually semi-enclosed, they offer shelter for ships in port, acting as natural harbors. Their river-to-sea connection allows ships to travel easily between marine and inland locations, facilitating the distribution of people and goods across large areas. Although airplanes, trucks and trains have provided new transportation options over the years, shipping--and estuaries--remain important to our economy. Even today, ships still carry the majority of the commerce in the world.


In addition to being economically important, estuaries are also critically important from an ecological standpoint. Estuaries are the meeting space of three very different habitats: marine, freshwater, and land. The mix of these three habitats creates a unique environment  - an environment which is challenging for some species, but ideal for others.

Rivers and oceans merge in estuaries, resulting in a combination of fresh and salt water, a mixture known as brackish water. The level of salinity (amount of salt) within an estuary varies by both location (areas closer to the mouth of the river are less salty) and time of day (twice-daily high tides bring salty water higher up into the estuary). Plants and animals that live in the estuary need to be able to tolerate fluctuating levels of salinity throughout the day.

The plants and animals closest to the shore must also be prepared to handle the tide-driven cycles of wet and dry. At high tide they are submerged under brackish water, and at low tide they are exposed to air. This is a particularly challenging environment to adapt to.


The species that are adapted to live in the estuary benefit from its exclusivity. Many species of marine fish rely on estuaries being inhospitable to predators, and they use the estuary as a nursery - a protected place to rear young.  Salmon are a good example. Salmon spend part of their life cycles in estuaries protected from larger fish and feeding on the estuary's bounty of small fish, crustaceans and mollusks to gain the size and strength needed to swim out to sea.

Estuaries on the coast of the Pacific Northwest provide much-needed habitat to keep salmon populations healthy. From California to Alaska, estuaries provide safe places for salmon smolt (young salmon) to grow and become ready to live for a while in the ocean’s salt water.


There are estuaries all along the Pacific Northwest coast. Some of the larger ones include the Columbia River that forms the border between Washington and Oregon, Washington’s Puget Sound, and the Fraser River in British Columbia. Alaska is also home to several large estuaries including the massive Yukon-Kuskokwim Delta and Prince William Sound.

Estuary in Port Frederick, Southeast Alaska

Estuary in Port Frederick, Southeast Alaska

The Panhandle of Southeast Alaska boasts a large number of estuaries. Scientists have counted over 12,000 streams flowing into 700+ estuaries in a territory only 500 miles long as the crow flies. But packed into those 500 linear miles are 19,000 miles of coastline that hug the nooks and crannies, islands, and bays of the contorted Southeast Alaska coastline. Given the density of estuaries, it’s not a coincidence that the largest salmon fisheries in the world are in Alaska.

In addition to the thousands of miles of coastline, there's another factor that contributes to the high number of estuaries in Southeast Alaska: the proximity of the mountains to the coast. Southeast Alaska is a rainforest, which means it receives lots of precipitation. Rainfall is immediately channeled down the steep inclines of the mountains without time to combine into larger rivers before being dumped into the ocean. The result of this rapid surface run-off of rain and snow is the perfect formula for the creation of estuaries - some relatively small and local, and some enormous in size and complexity.

In fact, scientists say that if we were to consider the entire Alexander Archipelago (another term for Southeast Alaska, like Panhandle) as one giant estuary, it would rival the Yukon or Columbia rivers—the 5th and 6th largest rivers in North America--in terms of water discharge.


Estuaries can be appreciated on many levels, including for their scenery. Some are mountainous, some are forested, some are flat as a pancake. Take, for instance, the difference in the three estuaries pictured below. Download the CoastView app to get a closer look at the variety of scenic estuaries that Alaska and the Pacific Northwest have to offer.

Kotzebue Sound estuary, northwest Alaska

Sixes River estuary, Oregon

Sitka Sound estuary, southeast Alaska