not necessarily, but usually, yes.
No, an estuary is where a river widens and flows into the sea.
it forms at the beginning of a stream or river
As far as I know, A river's mouth is simply called the 'river mouth'!
London is on the River Thames but not quite at its estuary.
The Estuary Delta
the largest estuary in Asia is the Obi river.
London isn't, but it is at the beginning of the Thames estuary.
The estuary of a river is where the tide meets the stream. A good sentence would be, the boy lost his hat in the estuary of the river.
Yes the Delaware Bay is an estuary.
The River Thames flows into it's Estuary between the Counties of Kent and Essex. This is where it meets the North Sea.
The river reaches the sea in its Estuary.
The Shannon Estuary is near Limerick, Ireland.