You got your story out of your head and onto a screen. That's more than I've managed. :-)
After the lake, there's a streamer in the top right. I go right, and see the streamer continue across the top. I go right again, and that was the room I got stuck in.
I think the problem was that I changed my vertical position, so I didn't find the trigger in the middle of the room. There should be something there to indicate that's where the player should go.