I am somewhat new to worldbuilding so forgive me if I am not as clear as I could be.
I have created a continent, but for relate-ability sake, imagine the US and Mexico, but where the Yucatan Peninsula peters off into Costa Rica, instead it widens back out into another large landmass. Looking at the Mexican map, right about where Coatzacoalcos is, and directly across the shortest point, the people of the northern side of that line plan to blow that land bridge to prevent the southerners from continuing to invade their country. (obviously with other security precautions in place to prevent attacks from the sea)
My original thought with this was that in blowing the land bridge, if the water levels change to become lower after that, it will reveal a lost island off the eastern shore of the northern land mass. Is this even possible? Or am I barking up the tree of fantastically far-fetched?
So I added my rough draft map. The area of land to be blown to smitherines will be in the middle of Serraud, the blue line between the two 'R's marks the line of detention. the small unmarked group of islands to the east in the ocean marked "Leeron" would be the so-called lost islands to be discovered if the water levels change.