Why are many of the world's largest cities built on estuaries?

Answer 1

Estuaries contain nutrients and support many organisms because there is plenty of light for photosynthesis. They foster plankton, which provides food for animals. Estuaries provide protected harbors, access to the ocean, and connection to a river. They provide food, wild life, and recreation.

Answer 2

Each town originally developed on a site giving two distinct values:

1) the river's lowest practicable bridging-point at thetime,

2) and the highest practical navigation limit for sea-going vessels, giving also a sheltered, easily-accessible loading / unloading dock.

At the timethe lower reaches of rivers were also valuablefor inland transport, soeverything came together to give the town's location.

As ships enlarged so the docks had to be moved further downstream, but this was balanced by developments in transport generally.