I'm so sorry. This is done using Channel Mixer, and I see from your profile that you have Photoshop Elements, which doesn't have Channel Mixer.
However, there are workarounds possible, in some cases.
I'll need to see more links to examples, though. That one is just darker, you know? It could be just as easily achieved with Levels.
I wonder if this is the kind of thing you've seen? The first photo is a colour original, the second is a standard black-and-white conversion, the third is a red Channel Mixer conversion:
Typically, red channel conversion tends to make blues (like water and sky) really dark.