The Hoosier Environmental Council estimates more than half of Indiana's streams and rivers would no longer be protected if President Donald Trump scraps the Waters of the U.S. rule.
Trump signed an executive order Tuesday that he says is "paving the way for the elimination of this very destructive and horrible rule."
The rule dictates which bodies of water are subject to federal clean water regulations. Indiana is one of several states challenging the current interpretation, which is under a stay.
The Hoosier Environmental Council wants the rule to stay in place. The organization says the regulations are necessary and took years to finalize.
"We feel it would be a waste of government resources to redo that work and rewrite it," says Indra Frank, director of environmental health and water policy.
But the Indiana Farm Bureau wants to see changes to Waters of the U.S. It says the rules place an unnecessary burden on farmers by forcing them to get permits for some daily activities.
"Saying you have to get a permit and you're going to follow this blanket, cookie cutter approach that [these activities] would generally fall under, I don't think it works," Director of Government Relations Justin Schneider said during an interview in December.
Schneider says changing or eliminating Waters of the U.S. would require starting a new rule making process.