The head of the Environmental Protection Agency told Congress Tuesday that her agency's bust of German automaker Volkswagen, and other high-profile cases, shows "America still needs an environmental watchdog with grit and teeth."

"Laws talk the talk; but enforcement walks the walk," EPA administrator Gina McCarthy wrote in an op-ed published Tuesday on The Hill newspaper's Congress blog.

"The bottom line is, strong standards are a key step — but it's our ability to implement those standards that turns promises of protection into a healthy reality for Americans," she said. "That's where the rubber meets the road."

McCarthy's agency is being sued by more than half the country's attorneys general, 15 large trade groups and number of other individual firms over her agency's climate rules. Republican appropriators are also targeting the EPA for large spending cuts that could hobble her agency's core mission.

McCarthy steers clear of these issues in order to reinforce where EPA thinks it has broad support to go after environmental violators: Volkswagen's scandal and a settlement over the 2010 BP oil spill in the Gulf of Mexico.

She said companies like Volkswagen "cheat on pollution control requirements threaten the health of children and the elderly."

"They violate consumer trust" and "skew the playing field for businesses that follow the law," McCarthy said. Volkswagen had installed "defeat devices" in its line of diesel sedans, where software activated pollution controls only when the cars were being tested for emissions, and switched them off while in normal driving mode. The violations will likely cost the company billions of dollars in fines from EPA enforcement action.

"Enforcement programs keep dangerous illegal activity in check," McCarthy said. "They hold violators accountable and deter bad actors."