From Mother Nature Network's Russell McLendon:

1972 was a watershed year for American water. That fall, an unusually unified Congress overrode President Nixon's veto and passed the Clean Water Act , a historic law that transformed the country's relationship with its water supply.

Forty years later, the law's legacy is hard to overstate. Not only did it empower the EPA to punish polluters, but it helped legitimize the young U.S. environmental movement at a key time in its history. River fires, toxic spills and other crises had cast a national spotlight on water pollution, spurring support for an aquatic sequel to the 1970 Clean Air Act. And unlike its precursor, the Federal Water Pollution Control Act of 1948, this law sought to make all U.S. waters "fishable and swimmable" by a specific deadline (1985), and gave regulators the tools to actually follow through.

"I've been at this game for a long time, and what I saw in wastewater discharges when I first started was so much worse than what I see today," says Ken Greenberg, chief of the EPA Clean Water Act compliance office for Region 9, which covers Arizona, California, Hawaii, Nevada, the U.S. Pacific Islands and 147 Native American tribes. "There is still work to be done, but it's a lot better than it used to be."

The CWA mainly targets big, point-source pollution like sewage leaks and oil spills, but it has also improved more than just water quality, says Bill Holman, director of state policy at Duke University's Nicholas Institute for Environmental Policy Solutions. "It's one of the most successful environmental laws ever enacted," he tells MNN. "The country has made huge strides in reducing pollution from wastewater treatment plants and industries, and it has even helped spark redevelopment of many areas, because waterfront property is valuable again. People like being close to clean water."

Yet as Greenberg and Holman both acknowledge, the CWA is still a work in progress even as it turns 40. An estimated 35 percent of U.S. waters are still unfit for fishing or swimming in 2012 despite the law's 1985 target of zero percent and it does little to control diffuse, "nonpoint" sources of pollution like urban stormwater and farm runoff. It's also beset by ambiguity, due partly to a series of court rulings that have raised doubts about which waterways are protected and which ones aren't.

"It's not so much that there's a flaw in the law, but there's a flaw in how it's being interpreted and enforced today," says Jonathan Scott of Clean Water Action, an advocacy group that helped design many of the Clean Water Act's original policies in 1972. While the law could use some updates, Scott tells MNN, its main problems come from 40 years of efforts to drain its funding and muddy its intent.

"What needs to happen first is a reaffirmation of the nation's commitment to the goals of the law: fishable, swimmable waters for all Americans," Scott says. "It has to start with making sure the law actually protects all of our water, not just some of it. To really protect one waterway, you have to protect everything upstream."

A Bridge Over Troubled Water
Before the Clean Water Act, only about a third of U.S. water was safe for swimming or fishing; the rest was fouled by sewage, oil, pesticides and heavy metals. The country was losing up to 500,000 acres of wetlands per year, and 30 percent of tap water samples exceeded federal limits for certain chemicals. All this began drawing national attention in the late '60s amid a series of dramatic news events, including:

• 1968: The insectide DDT appeared in 584 of 590 water samples taken by the U.S. Bureau of Sport Fisheries, some with up to nine times the FDA limit.
• 1969: The Cuyahoga River caught fire near Cleveland, Ohio, when a stray spark possibly from a passing train struck an oil slick floating on the surface.
• 1969: Discharges from four food-processing plants killed 26 million fish in one Florida lake, pushing the year's nationwide fish-kill total to a record 41 million.
• 1971: The FDA reported that 87 percent of U.S. swordfish samples contained so much mercury they were unfit for human consumption.

After four decades under the CWA, an estimated 65 percent of U.S. waterways now pass the fishable/swimmable test, while average wetland losses have fallen below 60,000 acres per year. And according to a 2012 EPA report , 90.7 percent of U.S. community water systems met "all applicable health-based standards" in 2011.

"There's a huge amount to celebrate in terms of progress," says Scott, who serves as communications director for Clean Water Action. "But at the same time, clean water is very easy for people to take for granted because of all the success we've had."

Crowd-Sourced Contamination
Fortieth birthdays often inspire a mix of fond memories and nagging regrets, and the Clean Water Act's big milestone is no different. Few who know the law neglect to sing its praises, but most make sure to mention its shortcomings, too.

"I would say it's a glass half-full/half-empty picture," says Robert Adler, an environmental lawyer who wrote a book about the CWA's 20th anniversary in 1992 and now teaches law at the University of Utah. While the CWA has been effective at reducing pollution from major sources, he says, "it has been less effective at curbing pollutants from nonpoint sources runoff from cities, farms, other intensive land uses. They have not been subject to nearly as strict a regulatory regime, and the typical assessment is those programs have not been as successful."

That's not to say the law ignores them, Greenberg notes, since the EPA does require general permits for certain sources of runoff. Construction sites may need erosion fences, for instance, while industrial plants and cities may need infrastructure to trap stormwater. "EPA can do inspections and enforcement, but we really require the industry to put in place best management practices," he says. "These permits are not as prescriptive because we're dealing with a more diffuse source of pollution."

The agency also has other tactics, like funding watershed-restoration projects that replace pavement with more permeable surfaces such as parks, ponds and green roofs, which let runoff stop running and settle down. "We're trying to promote different green infrastructure projects in cities to clean up stormwater, store it and concentrate it into groundwater, where it can be used as a fresh water supply," Greenberg says.

Such ideas are popular with many environmentalists, who want to see cities wield water more like nature does. "We have a linear system of managing water, and that's not sustainable," Scott says. "A better way is to keep more water circling in the area where it originates. It's just mimicking nature, mimicking what was there before we paved stuff. Those things reduce pollution, increase property values, and actually cost a lot less than paving and then treating the water when you collect it downstream."

So far, however, experts generally agree runoff has been the Clean Water Act's waterloo. "I think where the law has failed is in reducing runoff from cities and from farms," Holman says. "Agricultural practices were changing around 1972, and it has been less effective at dealing with some of the changes in the landscape since then." Urban runoff may contain a blend of many toxins, while farm runoff tends to carry nitrogen and phosphorus from fertilizers and manure nutrients that later accumulate downstream, fueling algae blooms that create low-oxygen "dead zones ."

Muddy Waters
Despite its failures in certain areas, the CWA has also faced accusations over the decades that it's too successful. Amid complaints from some industries and lawmakers that a broad interpretation of the law can force businesses to needlessly spend money on compliance, courts have issued a few restrictions in recent years.

In one 2006 case , the U.S. Supreme Court tried to clarify which waters fall under the law, limiting the phrase "waters of the United States" to include "only those relatively permanent, standing or continuously flowing bodies of water 'forming geographic features' that are described in ordinary parlance as 'streams ... oceans, rivers [and] lakes.'" The justices struggled to reach consensus, but their ruling did exclude many wetlands from protection, as well as some smaller or seasonal waterways. And earlier this year, the court also ruled that EPA decisions under the CWA can be challenged in court , allowing polluters to dispute the agency's authority rather than paying fines.

The EPA has pledged to work within the courts' constraints, but Holman says its pollution-fighting powers which it mainly passes on to states, along with resources and guidance are significantly weakened. "I think the courts have limited EPA's authority, and many states tie their authority to EPA's," he says. "In the case of wetlands, the Clean Water Act itself was pretty broad and could be interpreted expansively or narrowly, and the trend lately has been to reduce EPA's authority. And that has made it more difficult for EPA and states to do their jobs."

This is part of a long-running dance between courts and regulators, Adler says, in which neither wants to whittle down the law or leave it too broad. "We've seen kind of a cat-and-mouse game over the years, where the Supreme Court slaps agencies on the wrist, they go back and write more guidance and apply it to the statute, then it goes back to the Supreme Court again, and so on," he says. "So until Congress steps in and clarifies, or the agencies write more specific regulations that hold up in court, I fear we'll continue this game of going back to the courts every four or five years."

As for whether the Clean Water Act can threaten the U.S. economy, Adler is skeptical. "Anytime you're implementing a statute on a nationwide basis, you will have isolated cases where it's implemented too broadly," he says. "But in most cases, the vast majority of permits are granted. The system is designed to protect aquatic ecosystems in ways that don't impede businesses from operating."

Life Begins At 40
Aside from polluted runoff and legal ambiguity, experts also point to several other problems the Clean Water Act must contend with over the next 40 years including some it scarcely encountered in its first 40.

"While we've made a lot of progress in reducing the discharge of chemicals, there are also a lot we weren't aware of in 1972," Adler says. "You can't discharge any pollutant without a permit if it's regulated, but the bulk of our regulations are focused on a suite of chemicals that was compiled in the 1970s." Pharmaceuticals don't fall under the Clean Water Act, for example, nor do many hormone-disrupting chemicals like parabens and BPA . "There are whole categories of pollutants that have been little-studied and little-regulated," says Scott of Clean Water Action. "A lot of these substances end up in the water, and the law was not set up to regulate them."

But for the Clean Water Act to do its job, regulating more chemicals may not be enough, he adds. Like many environmentalists, he favors a more holistic approach to conservation. "If we care about water quality, we might also care what's coming out of the air and affecting our water," he says. "Our environmental and health laws are very compartmentalized Clean Water Act, Safe Drinking Water Act, Clean Air Act but the problems are all interconnected."

Holman also sees benefits to melding certain laws, noting how pollutants can shift around the environment instead of vanishing. "We're making great strides with the Clean Air Act, but a lot of the stuff that gets scrubbed out of smokestacks can pollute water," he says. "Having a more integrated policymaking approach would allow us to better weigh the different tradeoffs and make better decisions." Adler agrees, citing Congress' habit of drawing artificial lines in nature. "Why do we separate the management of water quality and water quantity?" he asks. "Why do we separate groundwater and surface water when they're hydrologically connected?"

But despite the potential confusion and loopholes, Adler also worries about losing what has worked. "What frightens me a little is the notion that we scrap the existing regulatory regime and start over," he says. "I don't want to throw out the baby with the bathwater." From a regulator's perspective, integrating laws may even be superfluous, Greenberg adds. "I suppose there are ways it could work, but we have plenty of chances to do that under existing laws," he says. "It comes down to people in my office working together water-division people talking to air-division people about a certain facility, that kind of thing. That's our primary strategy right now."

The Clean Water Act will likely remain clouded by debate for decades, from old issues like sewage and stormwater to emerging ones like fracking, rare earths and climate change . But on the 40th anniversary of such a landmark law, it's worth noting what it has clarified, too. And according to Greenberg, the CWA's legacy goes beyond reviving rivers, lakes and coasts it helped spark an environmental enlightenment.

"From my own experience, there has been a change in the environmental ethic of the general population, and the regulatory population as well," he says. "People are just more responsible about their environment. That's one of the real sea changes I've seen over the last 40 years."