Creeks, streams & rivers

What's the difference between a creek and a stream. Apart from the fact that in Australia we tend more to creeks than streams, which I've always assumed was just a terminology thing.

And who decides when a creek becomes a river? In northern NSW & Qld, some of the creeks are huge, way bigger than most rivers down south. So what denotes a river over a creek?

In the US, if memory serves, a length of moving water officially becomes a river when it reaches 100 miles.

Creeks, streams -- and more names for less-than-rivers, too. Becks...runs (as in Bull Run, Virginia)...branches...kills (this in New York State, e.g., Catskills)...burns (that sounds Scots)...rills. But the difference between them? Er, local nomenclature?