Fish happen to be a big draw for eagles in the winter months. Although they can hunt or scavenge for other things, their diet comes mostly from the open waters of rivers, lakes, and streams.
I should add the term “pirating” to the list of techniques used to get a meal. They aren’t above robbing or pillaging from another bird. In this particular instance, this chase on the Iowa river lasted over five minutes and reached heights of 800 to 1000 feet…in the end, the fish was dropped and lost…so neither eagle enjoyed the fruits of its labor.