While magma is generally preferred, it's becoming undwarven. You heard me. We're using magma as a crutch now. "How do we fix this? Oh right magma." No. Get creative. You're a dwarf, you have more than one tool and you can do things in any way you can push your migrants into dangerous constructions. Humans are the ones who use the same methods every time - nay elves are the ones who discovered wooden weapons and never changed. You, have an immense variety of tools that you leave collecting dust as you reuse the same one past the point over overuse.
There are only three ways to do anything in a river in DF.
1) Let winter freeze it.
2) Drain it.
3) Dump magma into it.
Drain it from the sides, by digging diversions.
Drain it from the bottom, by digging diversions.
Drain it from the top using pumps. All essentially the same.
Freeze it, easiest way of all. All very boring.
(Freezing, then building a constructed ice wall to dam it in summer, fun the first time.)
Magma is the most elaborate.
DF doesn't give us a way to, say, build a dam of corpses, or dump soap in to clog it, or build a tower above it then collapse it on top of the river.
(If constructions would do cave-in similar to natural rock, that would be cool.)
Our options are limited.
Trying every variation of implementation on them all is what's fun.
That said, have you ever used the magma method, or have you only used variations of the drain method?