I find this definition a lot more compelling than the one in the meme.
In other words it’s more to do with geology and how the wetland has formed from groundwater vs water flow, than it is to do with characteristics like ph and trees - those things sort of proceed from the basic structure.
It’s basically a bog with freshwater coming in through the bottom.
There are some in Massachusets, Colorado, Estonia, and this region of the UK called the Fens.