Just north of downtown — and a stone’s throw from the growling 5 Freeway — the concrete bed of the Los Angeles River gives way to soft earth and an explosion of riparian life: Cottonwood and sycamore trees push skyward, while fish dart beneath the swooping shadows of cackling waterfowl. The scents of mulefat scrub and sage hang in the air.

For many, it’s a vision of what the Los Angeles River looked like before it was transformed into a massive flood control channel. It also serves as a rallying point for those environmentalists who want to see the river returned to a more natural state.