Film buffs might recognize the Los Angeles River as the gigantic concrete gutter used for car chases in "Grease," "Terminator 2" and other movies. But the river is something else for U.S. EPA: "a traditional navigable water." EPA Administrator Lisa Jackson's declaration of the cement-lined channel today as "navigable" is aimed at allowing her agency to enforce Clean Water Act protections throughout the river's 834-square-mile watershed.