Rivers can't "want," Al. Rivers running free are the ones that don't have dams, weirs or constraining walls. So that means not all of them. An egregious example of a river stopped from running free was the Tees in glorious Upper Teesdale, dammed when Cow Green reservoir was constructed in the sixties. Two of England's finest waterfalls, Caldron Snout and High Force, were never again to enjoy their fearsome unpredictability, and some of England's rarest upland flora was destroyed. All in the name of progress. There was much outrage at the time but I haven't heard that a protest song was written about it.