These are beautiful Yellow Flag Iris (Iris pseudacorus) growing in a nearby wet-land. Unlike the Blue Flag Iris, which is native to the U.S. northeast, I. pseudacorus is a non-native, invasive plant. It is fast-growing and fast-spreading and can out compete other wetland plants, forming almost impenetrable thickets. http://aquat1.ifas.ufl.edu/seagrant/iripse2.html