Lake Okoboji in northwest Iowa

Many Iowans are headed to a public lake to mark the holiday and George Antonio of the Iowa Department of Natural Resources says the majority are man-made.

“Lakes that people would kind of know, their local lakes where they go recreate, about 65 percent of those in Iowa are constructed lakes,” Antoniou says. “The exception is kind of that northwest part of our state where you’ll start seeing some of those natural or prairie pothole lakes.”

Just 34 Iowa lakes are naturally occurring. The deepest natural lakes in the state are the system called the Iowa Great Lakes, surrounding the town of Okoboji.

“Going back in terms of history of our state, that would have been that region of the state that had glaciation and they call it the Des Moines Lobe and so that’s why you see natural lakes up in that northwest corner,” Antoniou says, “but when we start getting to the southern tier of the state, almost all of our lakes are constructed.”

The state has three large federal reservoirs built decades ago to control flooding. The Coralville Dam on the Iowa River between Cedar Rapids and Iowa City was completed in 1958 and created Coralville Lake. President Nixon was the keynote speaker at the grand opening of Lake Rathbun near Chariton in 1971. Sayloville Lake in the Des Moines River basin opened in 1977.