Have you ever seen a Water Bridge over a river......?
Pretty Cool

Have you ever seen a Water Bridge over a river?
Six years, 500 million euros, 918 meters long....This is a channel-bridge over the River Elbe and joins the former East and West Germany, as part of the unification project. It is located in the city of Magdeburg, near Berlin. The photo was taken on the day of inauguration.

Question:

Did the bridge have to be designed to withstand the additional weight of a ship and barge traffic, or just the weight of the water?

Answer:
It only needs to be designed to withstand the weight of the water! A ship always displaces an amount of water that weighs the same as the ship, regardless of how heavily a ship may be loaded.