Still a bit confusing though, what is a large amount of water, when is it small enough to be called a brook or stream. Then there are "Bournes" what are they?
In my own mind its any water that flows and eventually runs into the sea but there seems to be no definite measure of when its this or that.
Are drains, sewers and dykes not considered rivers in the close season and I have never established when an estuary is fresh water or sea. Its a messy old coconut.
That's rather the point made in various definitions, there is no particular size standard. As far as the names go, everything depends on location. There are a multitude of variations for a small watercourse depending on where in the world you are. Becks, brooks, burns, creeks, gills/ghylls, rills, etc etc. They aren't necessarily smaller than the watercourses deemed to be a river. The headwaters of many of my local main rivers are no bigger than a host of other small becks that join together to swell what will eventually become a decent sized river. There's little reason why one is designated as a river and the others not.
Locally, we have a few big becks (Cod Beck, Bedale Beck) that are as big, or bigger, than some of the named rivers (River Whiske). We also have the curious case of the River Ure which, for little obvious reason, changes into the (Yorkshire Ouse). I've seen suggestions that it's little more than a different dialect of the same word, but why and where the change applies is a bit of a mystery.
As far as the English/Welsh angling laws are concerned, as far as I'm aware, they simply apply the same rules to all waters that aren't truly enclosed, even if it's by sluices or locks. That's going to mean that there will be anomalies. Some canals are considered as self contained, others aren't. I'd guess that any drain, dyke or sewer that discharges water into the sea, or another watercourse that does, is likely to be treated as not being self contained. That doesn't make them rivers though.
