Even among Midwestern boosters, the Iowa Great Lakes may seem like a dry joke. Waterfront condos and nightclubs in rural Iowa? But the Okoboji that emerges from a horizon of dark green corn stalks in Northwestern Iowa (within a couple hours’ drive of cities like Omaha, Des Moines and Sioux Falls, S.D.) is less condos-and-clubs and more an oasis of American family vacations past.