How do I encounter on object on a scrolling background?

Hello All.
Making an aquatic-themed game. I’ve got my character riding a shark through the ocean no problem. But I need another sprite to appear as she goes along. It’s just a graphic indicating a sunken city below. The idea is that either the player would collide with it, or click on it, when it is encountered, and the next (underwater) scene would then open. I’ve tried having the second one as both a sprite and a tiled sprite, placed it at different points on the scrolling background, added the same event to it as the scrolling background, etc., but have not been successful in having the character encounter it. What is the proper way to do this?

Maybe you can change the opacity of your sprite or tiled sprite to make your sunken city,
And to change the scene as the Player clicks:
The cursor or touch is on City
Mouse Button is Pressed
Change the scene

Thanks, I’ll probably mess with the opacity of the underwater city so that it appears realistic. That’s something new, isn’t it? The main problem I’m having though, is that I just can’t figure out what to do with the sunken city sprite, so that the character encounters it. The character on her shark is actually sitting still, and the strip of ocean is scrolling by her, making it appear as though she’s moving through the water, all of which looks pretty good. But, as aforementioned, no matter whether I make the sunken city a sprite or tiled sprite, no matter where I place it, and no matter if I put the same event for the tiled sprite city as for the ocean (hoping they would move together), I cannot seem to get the city present in the “path” of the character. I’m definitely missing something! Is there some way to “attach” the city sprite to a particular point on the strip of ocean?