The latest attempt to do away with a federal water rule that protects millions of miles of streams failed Thursday, as senators couldn’t garner enough votes to override a presidential veto and block the contested Waters of the United States rule. The attempt to veto the rule, which protects bodies of water that provide drinking water for one-third of Americans, comes in the midst of a water contamination crisis in Flint, Michigan.

The vote was deeply divided among partisan lines, with 52 senators voting to upheld the veto, eight abstaining and the remaining 40 voting against it. While the vote was close, overriding a veto requires a super-majority. Senate Majority Leader Mitch McConnell (R-KY) filed for the vote, which was considered a long-shot from the start, less than a day after President Obama vetoed a resolution that would have blocked the water rule.

“Too many of our waters have been left vulnerable,” Obama said in a message to Congress. “Pollution from upstream sources ends up in the rivers, lakes, reservoirs, and coastal waters near which most Americans live and on which they depend for their drinking water, recreation, and economic development.”

The mandate, often referred to as the Clean Water Rule, was finalized in May after some eight years of design. It aimed to clarify what waters the Environmental Protection Agency can regulate under the Clean Water Act, experts told ThinkProgress. With its unveiling, the rule expanded protection to two million miles of streams and 20 million acres of previously unregulated wetland.

Before it, previous court decisions — including at least two Supreme Court rulings — made it unclear whether or not these waters could be regulated under the Clean Water Act. In turn, it was often difficult to address pollution problems in wetlands and other areas, as jurisdiction had to be determined on an almost case-by-case basis.

“And that’s a very time-consuming and expensive process,” said Victor Flatt, professor of environmental law at the University of North Carolina’s School of Law, in an interview with ThinkProgress.

However, how much clarity it created is in the eye of the beholder, said Craig Oren, environmental law professor at Rutgers Law School. “The rule is very controversial.”

Critics of the law have called the rule regulatory overreach, arguing that it is so broad that it covers seasonal puddles and dry creek beds. The agricultural industry has also opposed the rule, claiming that it would allow regulators to control irrigation ditches and seasonal ponds and tributaries.

The EPA denies these claims, arguing that the rule would not require any additional permitting requirements, and would preserve all existing exemptions and exclusions allowed under the Clean Water Act.

Many senators were resolute in their opposition to the rule Thursday.

“We have a choice today, we do have a choice. We can stand with our farmers, with our rangers, our small businessmen, our manufacturers, our home builders, or we can stand with an overreaching federal agency,” said Joni Ernst, the Iowa senator who introduced the vetoed resolution, prior to Thursday’s vote.

Congress’ attempt to undermine a major new provision of the Clean Water Act comes at a pivotal time for streams and water consumers. Water pollution has been under the national spotlight following a lead poisoning crisis in the city of Flint, Michigan. The lead emergency has stretched for months, infecting the blood of children and leaving tens of thousands of residents without safe tap water.

Thursday’s vote may not be directly related to Flint, but upholding the veto means the federal government is still entitled to protect streams that supply drinking water to a third of the country. “Flint does show, of course, that water is precious, and water supplies can be endangered and agencies have a lot of work to do,” said Flatt. “And if they don’t do their job, people can suffer — and that’s true about environmental issues, too.”

But although the Clean Water Rule was kept intact, experts said the law is still quite vulnerable. Congress could come up with another vote as Obama is nearing the end of his term and court challenges to the rule are almost certain.

“The administration that comes to power might seek to repeal this rule, or it might choose not to defend the rule in court against a challenge,” said Oren. “Of course [all] depends on what the courts say and what the election brings us.”