It took nearly a decade, but finally the waters left terribly muddied by two U.S. Supreme Court cases have gotten a good bit clearer.

This week, the Environmental Protection Agency and the Army Corps of Engineers issued a new rule clarifying which of the nation’s streams and wetlands come under the protections of the federal Clean Water Act.

Without this rule, some 117 million people – about one in three Americans – would continue to get drinking water from streams that lacked clear protection from pollution and degradation. And large populations of fish and wildlife would remain at risk of losing critical habitat.

The need for this clarification arose in large part from the U.S. Supreme Court’s 2006 decision in the Rapanos-Carabell case, named for the two petitioners who each had sought to develop wetland areas on their Michigan properties – one for a shopping center in Midland, the other for condominiums north of Detroit.

In a mixed ruling, the four conservative justices ruled that the Clean Water Act applies only to “permanent, standing or continuously flowing” bodies of water, casting aside the protection of ecologically crucial seasonal and ephemeral wetlands and streams that are often hydrologically connected to flowing waters downstream.

Four other justices disagreed with this hydro-illogical interpretation and sided with sound science and the overall intent of the Clean Water Act to “restore and maintain the chemical, physical, and biological integrity of the Nation’s waters.”

It was Justice Anthony Kennedy, however, who, in a separate opinion, introduced the confusing requirement that only streams and wetlands for which a “significant nexus” with navigable waters can be shown to exist should be subject to the law’s protections.

Justice Kennedy’s opinion set up a case-by-case approach that quickly became a regulatory nightmare and left in limbo the status of vast areas of small streams and wetlands.

Back in 2005, I joined nine other scientists, including the esteemed Harvard biologist E.O. Wilson, in writing and submitting an amicus curiae (“friend of the court”) brief to inform the justices about the relevant science in this case.

In the summary of our argument, we wrote:

“Reasonable people can disagree over language, and it is for the Court to decide questions of law. But when it comes to the connection of tributaries, streams, and wetlands to navigable waters and interstate commerce, there is no ecological ambiguity. In the opinion of Amici, if the Clean Water Act does not protect these resources, then it does not protect navigable waters from pollution, and it cannot achieve its goals.”

Besides underscoring the various pathways by which tributaries, wetlands, aquifers and rivers are connected, we pointed out that besides supplying water and fish, aquatic ecosystems provide valuable economic services. They recharge groundwater, filter pollutants, mitigate floods and droughts, purify drinking water, and sustain a diversity of habitats.

We noted that the loss of water-cleansing wetlands in the Mississippi watershed far upstream from the Gulf of Mexico can contribute to the formation of the low-oxygen “dead zones” that threaten the Gulf ’s fisheries and food webs each year.

We pointed out that interconnected wetlands and stream systems absorb stormwater, thereby alleviating flood damage.

With Republicans in the U.S. House of Representatives having already passed a bill that would roll back the new EPA-Army rule, and the Senate considering a similar measure, it is crucial for citizens everywhere to speak out about the importance of clean water and freshwater ecosystems to their health, communities and economies.

The EPA and Army Corps of Engineers have done a great service in clarifying the waters protected under the Clean Water Act, which enjoyed bi-partisan support and was signed into law by President Richard M. Nixon in 1972.

The new rule does not create any new permitting requirements, and it maintains all previous exemptions and exclusions, including for farm activities such as planting, harvesting and moving livestock.

But it removes uncertainty, unlocks regulatory logjams, and reinforces the critical role healthy freshwater ecosystems play in our economy and in building resilience against the more extreme floods and droughts coming down the pike.

Our government is the custodian of the public trust in water. Both sides of the aisle should respect and uphold the original intention of the Clean Water Act and leave this new water rule in full force.

Originally published at National Geographic Newswatch.