FLOATING about 150m offshore from Illinois Beach State Park, Hillary Glandon adjusted her scuba goggles, grabbed a small masonite plate from a nearby kayak and slipped beneath the surface of Lake Michigan.
The plate, called a Hester-Dendy sampler, helps biologists scrape algae off underwater rocks.
Just a few metres down, she reached a huge underwater ridge – limestone and boulders piled into long rows parallel to the coast.
On this late June dive, four scuba divers ferried equipment back and forth between kayaks and the ridges, collecting sediment and dropping off underwater cameras on the lake bottom.
Above them, a thick morning fog lifted, revealing clear blue water. From the surface, schools of juvenile fish could be seen darting in and out of sunlit patches along the ridges.
These are no ordinary reefs. Known as “rubble ridges”, they are entirely man-made.
“We just want to see, are these reefs impacting aquatic biodiversity as well as sediment retention?” Glandon said. “To get the whole picture of the aquatic community, we need to sample in different ways – not only sediments but the critters that live there.”
Artificial reefs are increasingly popular as fish habitats. But here, they are also designed to fight erosion.
Each ridge lies about a metre beneath the surface, breaking up waves during winter storms and slowing shoreline loss.
The gaps between them retain sediment without halting the natural flow of sand.
“The designers call it passive sand management – slowing erosion when it’s at its worst,” said Steve Brown, Illinois state geologist. “We’re trying to see, does it work like they thought it would?”
Glandon and her team at the Lake Michigan Biological Station, run by the University of Illinois, are studying the ridges as part of a federally funded pilot under the Great Lakes Restoration Initiative.
Installed at Illinois Beach in 2021 by the US Army Corps of Engineers, the ridges are being monitored alongside a second artificial reef at Fort Sheridan, as well as two control sites nearby.
The bottom of this stretch of Lake Michigan is usually flat sand – hardly attractive to fish or invertebrates.
But on her dive, Glandon found the ridges teeming with life: round goby that cling to rocky crevices, and shoals of alewife using the reef as a nursery.
“Lake Michigan is always changing, and it always will change,” said Philip Willink, a biologist with the Illinois Natural History Survey. “People don’t like that change. They want the shoreline in stasis. But how do we put that into city planning?”
Tracking shoreline changes
While divers sampled algae and sediments, other researchers stayed onshore, noting how the landscape had shifted since last year.
A boardwalk once jutting across the beach was gone, removed after waves battered it beyond repair.
“Every time I come back, it feels like something has changed,” said biologist Scot Peterson.
Erosion is visible everywhere on the Great Lakes, but Lake Michigan is particularly unpredictable.
Its levels normally rise and fall in 10–30 year cycles. Now, climate change is speeding that up.
In January 2013, the lake hit record lows. By mid-2016, it had risen more than a metre. By July 2020, it nearly broke the record high.
Such swings once took decades; now they happen within years, fuelled by heavier precipitation.
Today, levels hover around 176.5m, near the lake’s long-term average. Still, Illinois Beach State Park has been scarred: creeks have flooded, research buildings damaged, dunes stripped of grass.
In 2019, the Illinois Department of Natural Resources launched its biggest-ever capital project here: US$73mil for 22 stone breakwaters along 3.5km of shoreline. Finished in 2024, the barriers were paired with 12,000 cubic metres of new sand to bolster the beach.
But the massive project complicated the rubble ridge experiment.
“The rubble was supposed to be built further north,” Glandon said. “They moved it to accommodate the breakwaters.”
Early findings are mixed.
At Fort Sheridan, sand has built up. At Illinois Beach, erosion worsened between 2022 and 2024, though last winter saw little change.
“Sediment dynamics are hard to judge without a huge asterisk,” Glandon admitted.
Starved of sand
Illinois Beach’s 10.5km of natural shoreline is a rarity in Illinois, where most of the 100km of Lake Michigan coast is hardened with seawalls or breakwaters.
“Over thousands of years, the dominant current has moved sand southward,” said coastal geologist Liz Spitzer. “But human structures block the flow. You might build up sand in one place, but cause erosion right downstream.”
Brown put it bluntly: “Every time we create a structure, it stops the sand. You get erosion downstream. We haven’t sorted out how to live along the lake.”
The rubble ridges offer a compromise. Running parallel to the shore, they hold some sediment but still allow most sand to pass through, reducing the domino effect of towns building wall after wall.
At a cost of just US$1.4mil, they are relatively cheap.
“We want to give towns data and options,” Glandon said, “so they can retain some sand without hurting their neighbours.”
Building biodiversity
Invisible from land, the reefs are unmistakable underwater.
Rising from flat lakebed, they mimic natural shoals like Chicago’s Morgan Shoal – a remnant of ancient tropical reefs when the Great Lakes region lay south of the equator.
“Most of the lake bottom is sand or mud,” Willink said. “But reefs, whether natural or artificial, create nooks and crannies that support biodiversity.”
Preliminary data shows fish populations and diversity rising at both artificial reefs compared to control sites.
Underwater cameras, programmed to snap photos every five minutes, track fish density. Early results suggest the ridges serve as nurseries, with many small fish gathering there.
Invertebrates cling to the rocks too, forming the base of the food chain.
But too much trapped sand could smother these habitats — another reason researchers prefer reefs that don’t act like dams.
“A lot of what we’re facing in the 21st century is how to live with nature in urban areas,” Willink said. “It’s not just Lake Michigan. It’s everywhere.” — Chicago Tribune/TNS
