CHICAGO, Illinois — The Chicago river isn’t known for its fish — in fact, quite the opposite. It's been a dumping ground for everything from industrial waste to 800 pounds of human waste from Dave Matthews’ tour bus. But thanks to cleanup efforts, there are now fish in the river. And they’re at the center of a lawsuit that's pitting the state of Illinois against the Trump Organization.

The lawsuit, filed in August, revolves around Chicago’s Trump Tower. For years now, the building has been taking in close to 20 million gallons of Chicago river water each day to cool its air conditioning system.

While the practice itself isn’t unusual, environmental groups say the quantity of water the tower takes in, and then releases, is far larger than most buildings of similar size along the river. Moreover, the Trump Organization hasn’t performed the environmental assessments required under the Clean Water Act — assessments aimed at showing that the tower’s water intakes aren’t affecting local wildlife.

“We've stocked almost 300,000 native Illinois fish in this system, so if you're pulling that water in faster than our fish can swim, those fish can get killed in that system,” says John Quail, director of watershed planning at Friends of the Chicago River, one of the environmental groups involved in the state’s lawsuit. “So that's one big concern of ours.”

The Trump Organization didn’t respond to multiple requests for comment. But shortly after the lawsuit was filed, it told reporters that it was “disappointed that the Illinois attorney general would choose to file this suit,” adding that, “one can only conclude that this decision was motivated by politics." That analysis doesn't square with the facts of the case, says Mark Templeton, a law professor at the University of Chicago and one of the lead attorneys overseeing the lawsuit.

“They’re the second largest withdrawer of water from the Chicago River, and they are the only one of the top 15 who are not complying with the law,” he told VICE News. “So they can call it politically motivated if they want to, but it is environmentally motivated.”

To get a better look at the issue at hand, VICE News took a boat to Chicago’s Trump tower and used an underwater drone — at least, until the cops showed up.