Key thing there is is the "they have lots of rivers & streams filling fjords" bit. They also have much higher terrain than we have, making the energy on those streams and rivers much higher. And I think you'll find that they are much more sparsely populated than we are.Some countries e.g. Norway produce their electricity from renewable sources. Given they have lots of rivers & streams filling fjords, it shows it can be done.
We actually have few good sites for hydro - and most of them already have schemes running on them. The non-pumped ones suffer from running out of water in dry spells, the pumped ones act like big batteries and rely on something else low-carbon (eg nuclear) to "charge" them.
So we have a much higher demand, and far fewer (and lower grade) sites available - hence we don't have much usable hydro capacity.
Only in part - we use them because they work and are reliable. Nuclear can not be described as "easier" when you see the hurdles that have to be jumped to get a new plant off the drawing board.IMO we use fossil fuels & nuclear 'cos its the easier option.
People keep saying that, but of course, as stuff get "rarer" and the price rises, it then becomes cost effective to pull more stuff out of the ground. And there's a heck of a lot left down there yet.At some point fossil fuels will be exhausted, unless we've killed off the planet by then.