Why are waters near the Italian coast of the Adriatic Sea generally shallow?

The waters near the Italian coast of the Adriatic Sea are generally shallow because the coastline is characterized by low and sandy terrain.1

In contrast to the high, mountainous shores found along the Croatian and Istrian coasts—where sea depths are considerable—the Italian side of the Adriatic features a relatively straight, continuous, and low-lying shoreline. This relationship between coastal physiography and water depth is evident in areas such as the vicinity of Venice and near the delta of the Po River, where the adjacent sea remains shallow.1