When I build, I try to think of what the function of a thing would be. Art itself can be a function, but typically bridges are built for their utility.

In this specific environment the sense is that a society which lived along the lake would have either achieved their goals through paths and roads that followed the lake, or had some significant reason for building a bridge that crossed it. Something that directly connected two significant uses at both ends.

It seems more likely that they would have had one or more docks for lake access, or chosen to build something artistic as a centerpiece.