This flag uses a pall to represent the confluence of the Mississippi and Missouri rivers in the city, similarly to how the flag of Tuva represents the confluence of the Bii-Khem and Kaa-Khem into the Yenisei River, in their capital, Kyzyl. It’s things like this that make some flag design experts recommend that flags shouldn’t represent local bodies of water: it is very common for cities to be founded on confluences or forks.

Nevertheless, the flag of St. Louis is very distinctive and attractive, and I’d easily consider it to be among the best city flags of the Americas!