On Thursday, one of the country’s most effective environmental laws — the federal Clean Water Act — turned 40. [Americans] owe the law a huge debt of gratitude.

Its successes — bays that no longer are dead zones, far fewer beach closures because of sewage spills — didn’t simply happen. They required the combined efforts of government and public activists, and took considerable financial investment, along with excellent engineering and construction work, and leadership at multiple levels. But without the Clean Water Act, they couldn’t have been accomplished.

The act sets wastewater standards and regulates the discharge of pollutants into the nation’s oceans, rivers and lakes. Locally, one of the biggest focuses has been on coastal sewage treatment plants, which have upgraded their facilities and reduced by 90 percent the amount of sewage solids going into the ocean. Another local success has been with industrial waste programs, which have slashed their discharges of toxic metals and organic pollutants more than tenfold. Standards set by the act have led to cleaner beaches during the summer and the installation of more than 50,000 catch-basin screens and inserts to keep trash out of the ocean as well as lakes and rivers.

These measurable successes have reduced health risks to swimmers and surfers and improved ecosystem health. But they aren’t enough. The Clean Water Act as written can’t create the universally fishable, swimmable and drinkable (where appropriate) waters that Congress envisioned when it passed the act 40 years ago. It hasn’t been updated in 25 years, and it desperately needs to be.

Many kinds of pollution stemming from agriculture, mining, septic systems and the timber industry are still largely unregulated, and they are causing problems such as dead zones, hypoxic waters and harmful algal blooms in the nation’s waters. Storm-water pollution regulations also need to be strengthened. If you want to understand why, visit our local beaches after a rain. Many of them look like trash dumps, and about half of the county’s beaches get Fs on the Beach Report Card after a rainstorm. Polluted urban runoff is often toxic to aquatic life.

It’s no wonder that after 40 years, the Clean Water Act is in need of updating. We need storm-water pollution regulations that incentivize and require state-of-the-art technologies. We need infrastructure retrofits that will allow the capture and treatment of polluted runoff to the level required by water quality standards. And we need to upgrade sewage treatment plants to treat water to a level that can more easily augment local water supplies.

The question now is how to achieve these things. Some necessary fixes, such as tightening standards on storm-water pollution, can be accomplished through strengthening rules already mandated by the act. But other Clean Water Act modifications, such as regulating agriculture and mining, providing funding for green infrastructure projects or extending the act to cover groundwater, would require congressional action. In the current, highly partisan Washington atmosphere, that would be incredibly difficult to accomplish.

Still, polls consistently find a high degree of concern on the part of Americans about water quality issues, and most Americans value the protections that are in place. Representatives in Congress should listen to their constituents and move to finish the job of protecting aquatic life across the nation.

Without a more comprehensive federal approach to water management, the nation’s aquifers, rivers, lakes and coastal waters will continue to degrade. This isn’t simply an aesthetic or a tourism issue; clean water protects aquatic life and public health. Clean water is essential for drinking, and for agriculture, and for life. Congress had the foresight 40 years ago to override a veto by President Nixon to pass the Clean Water Act, which has served us well for four decades. Now the law needs updating to meet the act’s ambitious goals and serve us as well in decades to come.

Mark Gold, former president of Heal the Bay, is associate director of UCLA’s Institute of the Environment and Sustainability.