I read this article on 'the evils of dams' and how they're 'destroying the world' with their clean energy. The focus of the complaint was that dams create methane, which is a greenhouse gas that is far worse than CO2. This is, of course, ridiculous, as they don't 'create' methane but instead accumulate the methane creating organics already present in the water and concentrate them in one place (where it's no longer too diluted to notice).
Now, setting aside the nonsense that methane is a greenhouse gas (it's a thermal conductor which is often confused for a greenhouse gas) lets look at the problem again. The problem, as stated, is that the water pools behind the dam, like a P-trap under your sink, and it accumulates stuff that, if the dam wasn't there, would otherwise be flushed into the ocean, unnoticed and unseen. This accumulated organic matter 'rots' and puts off gas, one of which is methane.
Now, methane, when released into the air, is considered bad.
But Methane, delivered to your house in a pipe for cooking and heating, you can charge MONEY for.
Take a step back and look at the horrible horrible earth-ending problem that's "only solution must be the destruction of dams all around the world!" But this time, look at it as a glass half full instead.
It's rather simple to capture the methane and sell it when it's concentrated like this. And methane that is burned is turned into the much less dangerous CO2.
It's not economical to capture methane from a river or stream, but it is if you already have a billion dollar P-trap called a dam with complete control over how and where the water flows. Several models jump to mind, from dredging and a covered cesspool style (like farmers do with pig poop all the time), to an underwater or underground 'digester', to a passive system that pulls it from the water itself.
If the volume of methane is anywhere near the 'earth ending' levels they try to portray, then it's a goldmine, waiting to be tapped. And, as noted, it is 100% organic, would qualify as entirely carbon neutral (as the pig-poop example does), and could easily be a double green green win win... if politics wasn't always getting in the way.
Dams are highly political in that politicians get lots of money to pretend to hate them, and this methane complaint is just another twisted fact that as politicians aim and fire for their campaign donors, when in reality it is a goldmine waiting to be tapped.