What is an estuary? What is the difference between an estuary and a fjord?

An estuary is a partly enclosed coastal body of brackish water where a river meets the sea, forming a transition zone between river and marine environments. A fjord is a long, deep, narrow body of water in a U-shaped valley with steep walls, created by glacier activity. The key differences between estuaries and fjords come from their origins and environmental contexts. Estuaries are created by river flows and tidal actions, resulting in a mix of salt and fresh water, while fjords are formed by glacier activity, with deep waters and predominantly saline or sea water environment. Estuaries are typically rich in biodiversity due to nutrient-rich sediments, while fjords host unique ecosystems due to their depth and cooler temperatures.