Marsh by Sahayra

I saw this Scotch broom near location where we first met up as a group. It was very cynically chilling there as the invasive species that it is. I learned that its a very annoying plant from an awesome class member who's name has slipped my mind (sorry!). I think this organism as an invasive species may not have much of a ecological role other than invading other native organisms out of their place, which leads to having a negative impact on the wildlife habitat. The most interesting thing I learned was that there are salt water marshes in Washington… silly I know, but I really had no Idea and I think it was pretty awesome to have visited one.  Like I am genuinely amazed and plan on reading up on them, and the ecological system that they have going on. We may have learned about this in call already, but when Gwen said it during the trip I had a “OMG, what no way moment”. So now I’m all like “This is so cool” and i’m not really sure why, but my mind is amazed and so I shall not fight it. I now know that we have salt marshes in the pacific northwest, which has given me a cooler perspective about our area.
Can the organisms that live in the salt water marshes go from fresh to salt as they please? Especially since its where freshwater eventually meets with salt water? Or do they just stop swimming towards the areas with more freshwater?