ON A CHILLY DAY in early winter, a flat-bottomed skiff informally known as Simplicity cruises northward on the Willamette River from her launch in Sellwood. Thanks to post-Christmas snowmelt and winter rains, the river looks swollen and greasy, its milky, coffee-colored waters studded with floating deadwood. The kayakers, rowing teams, and powerboats that often turn this stretch of water into an aquatic playground are absent, leaving Simplicity to make a lonely chug toward Ross Island.

“Ross Island” is the collective name for a teardrop-shaped complex of four small islands—East, Hardtack, Toe, and Ross—that jut out of the Willamette just south of downtown. As we approach the islands’ southern reach, the shallow channel between East and Hardtack opens before us, bordered by dense, winter-barren cottonwoods and ash trees on either bank. With the glassy spires of the South Waterfront’s condo towers and downtown’s office high-rises looming in the background, this narrow passage looks like a portal to a lost world—some mossy, austere, primeval Northwest, unsullied by the dread fingerprints of man.

Ross Island’s history, however, is actually a dense collage of human intervention. A century ago, East Island did not exist. Likewise, Ross and Hardtack islands, now a unified wall of trees off the boat’s port side, were once separate. In 1927, the Army Corps of Engineers linked them with a skinny artificial land bridge that closed off the islands’ main channel. This rerouted the water flow so dramatically that a new silt deposit began appearing on maps soon after construction. The protuberance eventually grew into East Island, the lumpy quadrilateral of gnarly vegetation I see today. Meanwhile, poor Toe Island, once respectable enough, was whittled into a sad little rocky atoll that sometimes disappears beneath the waters completely.

As a complex, the island today is a strange combination of postapocalyptic wasteland and woodsy, rustic preserve. It’s festooned with hulking, corroding equipment and choked by invasive plants. Yet nature remains a partner in the island’s evolution in the form of a steady stream of visiting eagles and herons, deer and coyotes. It is this paradoxical capsule of wildness secreted in the city’s heart that the man standing next to me aboard Simplicity, Mike Houck, believes can become a green-urbanist gem of national, even worldwide, significance: a water-bound natural habitat as priceless to the lives of critters and the emotional well-being of humans as Forest Park.

“In this reach of the river, this is the most significant conservation opportunity we have,” Houck says. “And from a national perspective, I can’t think of another city that has anything like Ross Island in the heart of [it].”

Houck’s vision is simple enough. Ross Island sits just offshore from the 160-acre Oaks Bottom Wildlife Refuge, which Houck played a key role in creating in 1970. If combined into a single park, Oaks Bottom and Ross would amount to about 460 acres, or half the size of New York’s Central Park. A riparian refuge of that size would instantly become one of the world’s premier urban wildlands—over four times bigger than London’s Wetland Centre, which claims to be “the best urban site in Europe to watch wildlife,” for example. As an act of postindustrial reinvention, a revitalized Ross would rank alongside New York City’s transformation of the vast Fresh Kills landfill into a park-cum-nature reserve, a process that took 30 years.

But any restoration would also require an epic series of political, environmental, and engineering feats, likely stretching far into the future. For decades, the Ross Island Sand and Gravel Co ran the islands as a private industrial fiefdom, gouging out gravel to produce the concrete that built much of downtown Portland. Besides shearing off whopping chunks of the islands themselves, this mining past created a present-day regulatory tangle involving multiple tiers of government and a sometimes-obdurate company that still uses the islands as its primary factory. Add in feuding recreationalist factions—powerboaters and kayakers, two watery tribes who spar over wake zones and noise rules around Ross—and three different property owners, and some picture of the islands’ complicated status emerges.

Still, as I stand aboard Simplicity—with the silent islands on one side and a young bald eagle soaring above—it’s hard not to find Ross beguiling. If nothing else, a visit to this strange world fires the imagination.