An estuary is where a river meets the ocean. It is a body of water where salt water from the ocean and fresh water from the river mix together. Estuaries are the homes to thousands of animal and plant species. They are all over the world and at the end of almost every river. There are few rivers in the world that do not end up in the sea.

     Estuaries are based all around the world; they are even the main source of food for some cities. These cities build their homes, restaurants, and businesses around estuaries in certain areas of the world because of the environment it has. A big majority of the world gets their food supply and their water supply from estuaries, seeing that millions of cities around the world are based around rivers and eventually rivers lead into estuaries. Seventy-five percent of fish that people eat are caught in estuaries. These are just some of the reasons why they build their homes around estuaries.

     Estuaries are created by the tide. They are mixtures of salt water coming in from the ocean and fresh water entering the ocean from the river. The salt water is pushed under the fresh water causing an abundance of sea life to live in the estuary. Yet animals that live in the estuaries still have adapt to the water change caused by the tides. More on Salt in Seawater. They either have to leave the estuary at low or high tide, or adapt to both kinds of water. At low tide the water is mostly fresh water, and at high tide the water is mostly salty. Thousands of birds populate the area and depending on the food they eat they have to migrate maybe once, or two times a day. The tide changes twice a day and because of this fisherman also have to regulate their fishing around the schedule. So the saying nature prevails itself really adds truth to the state of an estuary.

     Rivers, by themselves, are also important in other ways. For example, they bring sand from inland to the ocean, which replenishes the beach that is washing away. "We could also rebuild rivers and guide them to places with a lack of sand, hoping that they will push the sand back into place." (Beaches). Because beaches are constantly washing away, this could become necessary in a few years. Another thing that rivers do is complete the water cycle. Water gets evaporated from the ocean, and rains on the land. Rivers carry the water back to the ocean. Rivers are also important to certain types of wetlands.