I can not eliminate the shoreline

[Neofita]

Just as in the topic.
I built a coastline.
Then I wanted to modify the site for development.
After the demolition, and improving the coastline.
I could not build because the old place was still.If you do not modify this area also can not build anything
Appears Information:"Affect the protected zone"
Help me pls    
Include photos.

[Rady]

Have you tried to use the "de-zone" tool (res/ind/com) on that area? Sometimes SC4 seems to "remember" that something had been built here recently ...