Supreme Court justices raised questions in February about the limits of government regulation of wetlands, canals and seasonal streams as the they heard oral arguments in two cases that test the scope of the Clean Water Act.

In both cases, landowners challenged the extent to which Congress intended to define “navigable waters.”

The Clean Water Act uses “navigable waters” to accommodate the Constitution’s Interstate Commerce Clause and identify wetlands under the purview of the Army Corps of Engineers and the EPA.

The court, in a case closely watched by environmentalists and property rights advocates, sought to determine whether the 1972 law should apply to some wetlands that are adjacent to tributaries connected to navigable rivers, lakes and other bodies of water or those separated by man-made berms.

Many states and environmental groups fear that weakening federal jurisdiction over waterways would limit the government’s ability to control pollution.

Within the Bay watershed, the states of Pennsylvania, Maryland, New York, Delaware and West Virginia, along with the District of Columbia, were among 34 states filing briefs in support of current interpretations of the government’s jurisdiction.

“Pennsylvania has a direct stake in the outcome of these cases because of the significant effect they could have on our ability to protect water supplies and keep our rivers and streams free from pollution,” said Gov. Edward Rendell when the state signed onto the brief earlier this year.

In a brief filed by the Chesapeake Bay Foundation, the group warned that under a narrow interpretation of the law, half of the stream miles and a third of the wetlands in the Bay watershed could lose federal protection.

“The protection of all wetlands, especially headwater wetlands is critical to our ability to restore water quality in our rivers, streams and the Chesapeake Bay,” the group said. “Without federal protection, the critical filtering capacity and habitat values are at risk.”

Studies have shown that headwater wetlands play critical roles in protecting water quality. Although states often regulate those areas on their own, many have said their programs would face intense pressure to weaken protection if the federal jurisdiction were lost.

In addition, if headwater streams lost Clean Water Act protection, the federal government could lose the ability to regulate discharges into those waterways, even though the pollution would still wash downstream.

During arguments on Feb. 21, some justices expressed concern that limiting the scope of the federal Clean Water Act might lead to the degradation of the environment.

Justice David Souter, questioning the attorney for one of the property owners, John Rapanos, suggested that limiting the law’s reach could allow an “end-run around the regulation” by polluters.

“All you have to do is dump the pollutant upstream far away from the watershed, and you get away scot-free,” Souter said.

But the government was questioned by Chief Justice John Roberts and Justice Antonin Scalia, who said an overly broad interpretation of the law might give regulators jurisdiction over storm drains and ditches.

“I don’t know how a storm drain is a water of the United States,” Scalia said.

Roberts told Solicitor General Paul Clement that “at some point the definition of tributary has to have an end” or it would go beyond the intention of Congress.

The Clean Water Act requires landowners to receive a permit from the Army Corps of Engineers before filling in waterways. The Corps has generally received wide latitude to prevent wetland degradation from regulations and court rulings.

But the Supreme Court in a 2001 case excluded “isolated” wetlands that don’t cross state lines and have no hydrological connection to navigable waters. In that case, the court ruled in favor of Chicago-area suburbs that wanted to build a landfill atop abandoned gravel pits that had filled with water and were being used by migratory birds.

The two cases before the court, both from Michigan, involve wetlands adjacent not to navigable waterways themselves, but to their tributaries. A woodlot owned by a family is a mile away from Lake St. Clair while the properties controlled by Rapanos are about 20 miles from a river that empties into Lake Huron.

A ruling is expected before the court’s summer recess.