Many players unable to place 2nd City Port in cityville, this is caused by limited area.. piers are only allowed on the original side it seem as well, this really limits a second city port
here’s a tips how to place your second city port in cityville :
The Cityville City Port can only be placed within certain areas of your city, namely the land facing directly out to sea on the half of your city that was available before the Platform Bridge was released. In addition, the area near the mouth of the river cannot be used nor can the City Port be turned around to be placed along the river itself.
You may want to move your Piers or Export Ports since these can be placed in more areas of your city along the water (although they still cannot be placed along the river itself). This should then free up the areas you can use to place your City Ports.