San Francisco

NEXT year will mark the 40th anniversary of the Clean Water Act, a milestone for a series of landmark environmental laws that began with the creation of the Environmental Protection Agency in 1970. Those actions set our nation on a course to restore our damaged natural resources, but today, because of political pressures and court rulings, the extent and durability of some of those key protections are at risk.

Since its enactment in 1972, the Clean Water Act has encountered resistance from powerful business interests that have tried to fill wetlands, drain marshes, develop shorelines and allow pollution to flow off their property. One approach these developers have used to weaken the law has been to try to limit its jurisdiction, to say it shouldn’t apply to this or that water body. The rationale has always been to argue that the water on the particular property in dispute didn’t connect with interstate bodies of water and therefore should be exempt from federal regulation.

When the act became law, two-thirds of our nation’s lakes, rivers and coastal waters were unsafe for fishing or swimming, and untreated sewage and industrial waste was routinely dumped into our waters. The law was partly a response to the shock the nation experienced when the filthy Cuyahoga River in Cleveland erupted in flames. Since then, industrial pollution has declined significantly. Fish have returned to countless water bodies that were once all but lifeless. Progress has come in fits and starts — despite more litigation filed than the law’s proponents expected or wanted — but it is real and evident.

Still, there are reasons for concern.

One is the ambiguity introduced by two Supreme Court decisions — Solid Waste Agency of Northern Cook County v. Army Corps of Engineers in 2001 and Rapanos v. United States in 2006 — over which American waters fall under the law. The law was intended to protect “all the waters of the United States.” But the decisions can be taken to suggest that the law does not protect certain waterways — those that are within one state or that sometimes run dry, for example, and lakes unconnected to larger water systems. As a result, fewer waters are protected, and those who wish to build on land that requires dredging and the depositing of the fill elsewhere face confusion, uncertainty and delay as federal regulators try to determine which water bodies fall under the law.