Five Major Types of Estuaries — Reading Comprehension

Estuaries are places where freshwater from rivers meets saltwater from the ocean. Not all estuaries are the same—scientists classify them into five major types, based on how they are formed.

1. Coastal Plain Estuaries
   These are formed when rising sea levels flood river valleys. The Chesapeake Bay is an example. They often look like wide, drowned river mouths.
2. Tectonic Estuaries
   These are created when land sinks due to movements of Earth’s crust. The San Francisco Bay is a tectonic estuary. They usually have deep basins.
3. Bar-Built Estuaries
   These form when sandbars or barrier islands block part of the coast, trapping water behind them. The Outer Banks in North Carolina are an example. They often look like long, shallow lagoons.
4. Fjord Estuaries
   These are formed when glaciers carve deep valleys that later fill with seawater. Fjord estuaries are very deep and narrow, with steep sides. They are found in Alaska, Norway, and New Zealand.
5. Delta Estuaries
   These form where large rivers deposit sediment at their mouths, creating branching channels. The Mississippi River Delta is one of the best-known examples.

Each type of estuary has a unique structure, but all share important functions: they provide habitat, filter water, and protect coasts. Understanding the types helps scientists and students see how Earth’s processes shape ecosystems.

Fun Fact: Fjord estuaries can be so deep that little sunlight reaches the bottom, creating a mysterious, dark environment!

Which estuary forms by flooding rivers?

What caused tectonic estuaries?

Which estuary is like a lagoon?

Where are fjord estuaries found?

What builds delta estuaries?

San Francisco Bay is an example of?

Why are fjord estuaries dark?

Which estuary is made by barrier islands?