The wide part of a river where it meets the sea and fresh water mixes with salt water. It is often rich in wildlife and important for both nature and human activity.
From Latin *aestuarium* 'tidal marsh, channel', from *aestus* 'tide, heat'. It originally referred to places strongly affected by the tide.
An estuary is like a borderland between river and ocean, with water that’s not quite fresh and not quite salty. These mixing zones are some of the most productive ecosystems on Earth, feeding birds, fish, and humans. The word hides the idea that edges—where two worlds meet—often teem with life.
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