The design, known as "Sunrise Over the Lake", was designed by Robert Lenz. He explains it this way:
The sun rising over Lake Michigan symbolizes a new day. The blue bars in its reflections represent the city’s three rivers and founders.I'm working on some updated renderings of the 1897 contest winners, and hope to shortly combine my past posts into one comprehensive history of Milwaukee's flag. Until then, congratulations to Mr. Lenz!