Canada Has a New Forested Floating Island. Scientists Think It Used to Have Many More.

A few weeks ago, while out boating in British Columbia’s Williston Lake, boater Rocky Avery stumbled upon a previously uncharted island. It was about the size of two U.S. football fields and covered in lush trees.

It was also floating.

The video Avery shared and that CBC first reported on shows the verdant mass bobbing and rippling in the blue water as waves passed underneath it. After the initial discovery, he lost track of the island for a few weeks, before spotting it again in late August.

It’s “a phenomenal sighting,” said Rebecca Helm, a marine ecologist at Georgetown University. Such big, forested floating islands are “rare for our modern age,” but were once more common before people routinely dammed rivers on industrial scales and logged vast swaths of the continent.

“This island feels more like an old ghost than a shocking new occurrence, something humans used to see much more regularly,” Helm said.

Floating Flora

Many floating islands are a combination of aquatic plants, root masses, some soil and woody debris — light material that can stay afloat — and are often found near wetlands or bogs. The plants’ roots, seeking sunlight and nutrients, wind through the water and weave a dense, tangled mat of vegetation.

When the water level suddenly changes or a storm hits, the mat can detach and float away, creating a floating island.  Water levels in Williston Lake were extremely high in August, which could have triggered this island’s maiden voyage.

Dozens of similar islands can be found around the world. They’re a nuisance on Lake Victoria in Africa, blocking navigable waterways and choking up hydropower dams. They get pushed around by boaters in Wisconsin. And they can bring tourists, as with one island in Italy that is said to have been visited by Pliny the Elder.

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The islands can fall apart in days or persist for years, or even longer. But the Williston Lake island, with its seemingly intact forest, may be built a little differently. Without stepping “ashore” on the new island in Canada, it’s hard to say for sure what its composition is, said Natalie Kramer Anderson, a river researcher and National Geographic Explorer who spent years studying massive log jams in the Northwest Territories. These are “jaw dropping” deposits of driftwood that accumulate over decades, or even centuries, and can cover up to 20 square miles.

While researching those massive log jams, Anderson saw firsthand how wood-based floating islands might form. When trees fall, some land in rivers and are carried along as driftwood until they’re deposited on a river bank or lake shore. Seasonal flooding can deposit them into driftwood rafts and mats, which serve as a foundation for soil to accumulate and for new trees to take root in.

Anderson recalled once walking across a sea of driftwood, dotted with seedlings, and taking a core sample of a mature spruce. “As I was coring the tree, I noticed there was water flowing underneath it,” she said. “These were 50-year-old trees. They were basically just growing on the log pile” — a floating tree nursery. It was still attached to land, but Anderson could easily imagine how a driftwood raft could similarly develop in a calm spot along a lake shore.

Anderson was then pleasantly surprised to find out about the Williston Lake floating island, which most likely came from the lake's long shoreline, loosened by strong waves, winds, and the recent water level change.

“It’s really exciting,” Anderson said. “People today haven’t seen anything like it before.”

Endangered Islands

For Anderson and Helm, the forested floating island isn’t a novelty. It’s an endangered landform. Such islands might have once been common sights in British Columbia and beyond, including on the open ocean. But then, as more rivers were dammed and more trees logged, rivers transported less wood downstream, providing less fodder for floating islands. People also remove log rafts from waterways to keep them clear for economic and recreational opportunities. “We’ve changed so much of the processes that form them,” Anderson said.

To better understand how this island came to be, Anderson would be like to see researchers date the trees, to see if there’s an older core or if they’re all the same age. They may have a chance to. The CBC reports the island had been found landed ashore about 18 miles from where it was last spotted. And as Anderson pointed out, with the dam downstream, “the island doesn’t have anywhere to go.”