In 1769, Spanish explorer Gaspar de Portola rode his horse across a wide plain punctuated with rolling hills leading to a half ring of sharp peaks. Portola, as the governor of Baja and Alta California, was on an expedition to extend the Spanish influence northward, scouting potential locations for missions and towns. When he came upon the intersection of two streams, flowing south toward the Pacific Ocean, Portola made a note, and future Spanish settlers would christen the site “El Pueblo de la Reyna de los Angeles.” The seed of the modern day Los Angeles megalopolis had been planted.

Today, the confluence is a concrete encrusted afterthought and the starkest example of the changing – some would say misplaced – priorities that have marked L.A.’s transformation over the last couple of centuries. The channelized river represents two of the city’s environmental blind spots: the subsuming of nature by a growing population, and the ever-present threat of a water shortage. L.A. expends enormous political and economic capital to gather water from across the American southwest while its own runoff is whisked unceremoniously to the sea.

But in recent years, a growing community has sought to reverse the trend and reconnect the city with its natural heritage. An important faction of this movement was on display last Monday at a UCLA-based screening of Rock the Boat, a documentary that follows a group of rebel kayakers on its quest to paddle all 51 miles of the L.A. River.

The outing was part publicity stunt, part reasoned activism. Legal jurisdiction over a body of water is determined by its use; “navigable” waters are the domain of the federal government rather than state or local agencies, and are thus subject to federal laws. Environmentalists – former U.S. Army Corps of Engineers employee Heather Wylie most vocal among them – have long sought federal protection for the L.A. River. If only the waterway could be proven navigable, the thinking went, then laws like the Clean Water Act would be brought to bear on industrial polluters, and the river could be set on a path toward recovery.

What better way to demonstrate navigability than to, well, navigate it?

Access to the river is generally forbidden, but with a documentary crew in tow and a liberal interpretation of their filming permit, Wylie, kayaker George Wolfe, and about a dozen adherents paddled the length of the river over three days. Their efforts were rewarded when, two years later, the EPA cited the expedition in its official endorsement of the L.A. River as a navigable waterway.

Now, with legal momentum and a feature-length documentary – a rare example of an action-minded film whose self-righteousness doesn’t block substantive progress – the river’s future is brighter than ever. Selected portions of the waterway are open for recreation during the summer, including the newly accessible Glendale Narrows, as mandated recently by the L.A. City Council.

The progress is expected to continue, if not always at the pace that all activists might prefer. As stated in the City’s River Revitalization Master Plan, “the River’s ecological and hydrological functioning can be restored through re-creation of a continuous riparian habitat corridor within the channel, and through removal of the concrete walls where feasible.” The plan is careful to note, however, that the last several decades of Army Corps of Engineers effort will not be completely dismantled. “If one completely restored the River to a naturalized condition throughout its entire length, it would be very difficult to achieve flood control requirements and maintain current urban development.”

Nonetheless, the progress on the L.A. River is an encouraging case of waterway reclamation, a trend that has gained momentum with the application of pollution laws and the removal of dams. To Rock the Boat director Thea Mercouffer, it’s an example of “how a group of people not necessarily trained as activists can claim back their commons.”