A historic return to the river

For the first time in more than a century, a lake sturgeon has been tracked as far upstream in the Milwaukee River as Ozaukee County — a long-awaited measure of success for efforts to rehabilitate the population of the ancient species, create fish passages that open spawning grounds and improve the quality of the river water and habitats.

“This is truly a historic day for a historic fish, the lake sturgeon, thanks to decades of bold and innovative efforts and the investment of many agencies and individuals to restore this native fish to the Milwaukee River,” said Ozaukee County Director of Planning and Parks Andrew Struck, whose department leads the Ozaukee County Fish Passage Project.

The sturgeon that made history on March 30 by swimming through a fishway to navigate around the Mequon-Thiensville Dam and continuing upstream is no stranger to those leading efforts to reintroduce the lake sturgeon to the Milwaukee River and open spawning grounds for the native species.

The 50-inch-long male was stocked in the river during the 2011 Sturgeon Fest in Thiensville as part of the Return the Sturgeon Project led by the Wisconsin Department of Natural Resources in partnership with Riveredge Nature Center in the Town of Saukville. 

The project is responsible for stocking more than 22,000 lake sturgeon  — about 1,000 a year — in the Milwaukee River, where the fish, one of the largest freshwater species in North America whose origins date back at least 150 million years, was rendered extinct by the early 1900s due to overfishing, habitat degradation, pollution and dam construction.

The sturgeon stocked as part of the program are raised in river-side pens filled with river water, which allow the juvenile fish to undergo the process of olfactory imprinting, essentially memorizing the unique chemical and mineral signature of that water. 

After being released, the young sturgeons make their way downstream to Lake Michigan, where they live the majority of their long lives. 

The typical lake sturgeon grows to between 4 and 6 feet long, weighs 30 to 80 pounds and lives to be 50 to 100 years old. The oldest and largest lake sturgeon grow to 7 feet long, weigh 200 to 300 pounds and live to 150 years old.

When sturgeon become sexually mature at 15 to 20 years old for males and 20 to 25 years old for females, they use their olfactory senses to return to the tributaries where they were raised to spawn.

“It’s really quite amazing that fish that have been gone for more than a decade know exactly which river is theirs and return,” Struck said, although he added it is not unlike migratory birds that return year after year to the same nesting sites after traveling thousand of miles on their seasonal journeys.

The detection of the sturgeon last week indicates that the stocked fish have successfully imprinted on the Milwaukee River, and program managers have reason to believe the fish was not an aberration. Days after the first sturgeon was tracked going through the Mequon-Thiensville Dam fishway, a second one was detected navigating around the dam, Struck said.

“He’s not alone, which means he’s not an outlier,” he said. “He has friends.”

Key to the stocking program is a tracking system that allows researchers to identify and follow sturgeon that have returned to the river after spending more than a decade in Lake Michigan. Every stocked fish has a passive integrated transponder, which Struck said “is very much like the chip in pets,” that is recorded by sensor arrays on the river bottom. The Mequon-Thiensville Dam also has an underwater camera that recorded the sturgeon that passed on March 30.

Although that fish made history by traveling upstream of the dam, it is not the first sturgeon stocked in the river to return to it. In 2021, three sturgeon, one of which was raised at Riveredge Nature Center, were detected and captured in the river in Milwaukee County. In fact, the sturgeon who made history last week was detected in the river in 2024 at the Urban Ecology Center in Milwaukee but no further upstream.

The success of the Return the Sturgeon program hinges on allowing the sturgeon to reach the best spawning grounds miles up river in Grafton, and that is where the Ozaukee County Fish Passage Project and similar efforts in Milwaukee County have proven critical.

What Struck described as the “massive, multi-agency effort to removal impediments and barriers to fish passage and restore aquatic connectivity along the Milwaukee River” began with the remove of the North Avenue Dam in Milwaukee in 1997 and has resulted in the reopening of 31 miles of river between Lake Michigan and Grafton.

Also in Milwaukee County, the Milwaukee Metropolitan Sewerage District led efforts to remove the Estabrook Dam in 2018 and install a fish passage at the Kletzsch Dam in 2023.

Key to ridding the river of barriers in Ozaukee County was the removal of Grafton’s Lime Kiln Dam in 2010 and construction of the fishway at the Mequon-Thiensville Dam the same year as part of the Planning and Parks Department Fish Passage Program, which has invested $25 million — $2.5 million in the fishway alone — in primarily grants and donations in removing impediments in the river and its tributaries.

The fishway, a meandering, stream-like channel that allows aquatic life to bypass the 6.5-foot-tall dam, underwent extensive reconstruction in 2021 and 2022 so it could accommodate larger fish species, specifically sturgeon,  Struck said.

“It looks like it works,” he said.

The sturgeon that make it past the Mequon-Thiensville Dam will only be able to swim upstream as far as the Bridge Street Dam in Grafton, but that is far enough to reach prime spawning grounds, Struck said. 

“We know the area where the Lime Kiln Dam was has some of the best sturgeon habitat,” he said. “But while we know it’s suitable, we want to determine if it’s enough.”

The identification and enhancement of sturgeon spawning habitat has been the focus of a partnership between Ozaukee County, the University of Wisconsin-Milwaukee and the DNR. 

The goal of that partnership, as well as the Fish Passage Program and Return the Sturgeon effort, is to give this ancient species that was once wiped out in the river what it needs to reproduce successfully there again, and researchers say the fish that made it into Ozaukee County and through the fishway is one big step toward that goal.

“This historic event represents a critical step toward establishing a self-sustaining lake sturgeon population in the Milwaukee River,” Aaron Schiller, a DNR fisheries biologist, said. 

That historic event, which came 20 years after the Return the Sturgeon effort began and 17 years after Ozaukee County launched the Fish Passage Program, was a long time in coming but worth the wait, Struck said.

“We’re absolutely thrilled,” Struck said. “It’s been a lot of work by a lot of people over a long time.”