I was being shown a new hydro plant at our local river a few days ago (From
the outside) The Project Manager was saying that the speed was finely
regulated by the water flow to give the right frequency. (That was as
technical as he could go on the topic).

This meant that in time of high flow it is throttled back considerably.
Isn't it possible to generate DC and convert it electronically to AC?
Wouldn't this mean that higher speed would give more amps?