The phrase "city of lakes and prairies" is a unique and descriptive way to refer to a particular place. Synonyms for this phrase might include "water and grassland metropolis," "hydrated and flatland municipality," or "lake and plain town." Other options could include "aquatic and meadow urban center," "reservoir and savanna city," or "pond and steppe hub." These synonyms convey a sense of both the natural features and the urban environment of the location in question. They could be used in a variety of contexts, from tourist brochures to news articles to marketing materials.