A television station in Cedar Rapids has received several photos and a video showing what some believe to be a shark swimming in the Mississippi River near Harpers Ferry, Iowa.
A bull shark is the only shark capable of surviving in freshwater, but would a bull shark have made a 1,000-mile-plus swim up the Mississippi River from the Gulf Coast?
The answer: doubtful.
Andy Allison of the National Mississippi River Museum and Aquarium told KCRG that a bull shark could withstand the freshwater to make the trek but would struggle in the water's chilly temperatures.
And another thing, the fin doesn't fit the description.
"The shape is not consistent with the fin shape of a bull shark," he told KCRG, explaining that bull sharks have a straighter fin and this one is curved.
That's not to say Iowa has never had sharks. The state had a lot of them back when Iowa was down near the Earth's equator, covered in ocean, hundreds of millions of years ago.
Geologists know this because they've found shark remains in the rocks.
"Right around 345 million years ago,” said Ryan Clark a geologist with the Iowa Geological Survey. “We do have some actual shark teeth—looking things in some of the rocks."
So if it's not a shark, what could it be? Some suggested it could be the fin of a large grass carp, but Allison had a more logical answer.
"To me that picture looks like a piece of driftwood floating down the river."
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