Mark Hoffman Postdoctoral student Dirk Koopmans (right) prepares to haul aboard a piece of equipment used to monitor conditions on the bottom of Green Bay, which is suffering from an oxygen deficiency. UW-Milwaukee faculty member Jerry Kaster (left) watches and Geoff Anderson operates the winch.

Nearly 400 years after French voyageur Jean Nicolet arrived with a bang on the banks of lower Green Bay — he fired two pistols skyward to announce the white man's arrival in the world's largest freshwater estuary — the same stretch of shoreline was the scene of another fateful landing.

Phones at the Wisconsin Department of Natural Resources started ringing in early August 2005 with an outrageous tale of a mass migration of fish from the center of the bay to its rocky beaches.

"The report from the caller was 100,000s of dead and dying small fish nosed up against the shore," Paul Peeters, a DNR fisheries biologist, reported in an email to his bosses at the time.

Peeters tossed his boots, nets, gauges and a clipboard into his truck and drove a half-hour south from his office in Sturgeon Bay to Bay Shore Park and found that the reports had not been exaggerated. The fish were so thick he could see nothing at the shore but mottled flesh.

And eyes.

All the live fishes' heads were, oddly, pointed in the same direction: east. Toward land.

"The fish were actually trying to come up out of the water," Peeters observed in the email. "One of the neighbors had actually used a leaf blower to blow them back into the water!"

The mystery only thickened when Peeters dipped a probe in the water to take temperature and oxygen readings. Air temperatures had been in the 90s that week, and he was expecting to find water temperatures at this shallow end of the bay in the 80s.

The probe told a different story. It was a bone-aching 61 degrees.

But the water wasn't just cold. It was deadly.

The oxygen reading Peeters got was so low it indicated the fish had literally been suffocating. Imagine a toxic wind blowing across Milwaukee that pushed desperate, choking people to seek refuge under the surface of Lake Michigan. That, in reverse, was apparently what had happened to these fish so bent on leaving the water.

"They were up tight against the shoreline," Peters wrote. "Nose to nose, shoulder to shoulder."

By all accounts, everything had been fine the day before — no fish clustered at water's edge; cottage owners in the area said they had been swimming in nearly bathtub-warm water.

Peeters netted 69 struggling fish and drove them back to his office, where they were packed on ice and sent to the state fisheries lab in Madison for tests to determine how something so ghastly had happened overnight.

An ecological treasure trashed

Nicolet had been seeking a legendary shortcut to Asia in 1634 when he led the first European expedition to the western shore of Lake Michigan.

The explorers paddled down the western side of the Door Peninsula into an embayment and river system teeming with wild rice, wild celery, waterfowl, beavers and fish — lots and lots of fish. Whitefish, herring, pike and pickerel. Catfish, suckers, bass and sturgeon.

The fresh waters of Lake Michigan and Green Bay made it clear to Nicolet and his canoeing crew that they had not crossed the ocean and landed in the Far East. But he nonetheless donned an Oriental silk robe when he stepped ashore, where he was met by hundreds of curious members of the Winnebago tribe.

"Nicolet reported to his superiors that he was well entertained with 'sixscore beavers' being served at one banquet," reads a plaque near a statue in the area commemorating his arrival. "But it was the pelts and not the flesh of the beaver that were to be highly prized by those who followed him."

Indeed.

Green Bay, its wetlands and nearby forests subsequently endured centuries of over-trapping, over-logging and overfishing. By the 1800s, commercial fishermen pulled millions upon millions of pounds of whitefish, herring, lake trout and perch annually from the bay. They were so convinced of the bay's endless bounty that they considered sturgeon a nuisance in their nets. The prehistoric fish, which can live longer than a century and grow to several hundred pounds, became so reviled they were stacked like cordwood on the shore of the bay until they had dried enough to be set ablaze, sometimes as fuel in steamship boilers.

After the trappers, timber barons and fishermen had their way with this remarkably resource-rich pocket of the New World, industry moved in. By the 20th century, the bay's main tributary, the Fox River, had become home to the largest concentration of pulp and paper mills in the world.

Water pollution in the river and bay was so bad by the 1970s that it was common for parents to forbid their children from dipping even a toe in the fetid flow. Kids found other ways to play. They plucked nuggets of sulfur from the riverbanks (a product of the pulp-making process) and lighted them afire so they oozed like lava with nostril-stinging fumes.

Photo Gallery The sewage plant for the Green Bay Metropolitan Sewerage District, or NEW Water, sits where the waters of the Fox River flow into Green Bay. The sewerage district is facing hundreds of millions of dollars in treatment plant upgrades under a new state plan to reduce the amount of phosphorus flowing into the river and bay. Photo Gallery: Researchers study 'dead zones' in Green Bay

Things have gotten dramatically better since passage of the Clean Water Act in 1972. Paper companies installed strict pollution controls. Cities and towns spent hundreds of millions of dollars on sewage treatment upgrades. It's why the lower Fox River today supports some 35 species of fish.

State Sen. Rob Cowles, a 64-year-old Green Bay native, remembers his own childhood trips down to the banks of the Fox. The only fish he saw were floating carp carcasses.

"When I was a little kid playing down by the river with friends, there was simply nothing," he says. "Nothing."

Now when he drives over the De Pere bridge several miles upstream from where the river flows into the bay, he is amazed at the dozensof fishing boats in front of a paper mill that happens to bear Nicolet's name.

Yet troubles have endured.

The swimming area at Bay Beach Amusement Park, near the mouth of the Fox River, closed due to pollution during World War II and remains closed today. The City of Green Bay's drinking water comes from neither the river nor the bay; it is piped over from the main body of Lake Michigan some 30 miles to the east. The Fox River might now yield trophy-sized walleye, but their flesh is so laced with 20th century paper mill pollutants that the biggest catches remain too toxic to eat.

Still, by many measures, water quality in the river and lower Green Bay had improved significantly since the early 1970s.

And then thousands of fish beached themselves at Bay Shore Park.

Dead water, dead fish

Peeters, the biologist, had a theory about how the fish died.

Anatomy of a 'dead zone' Algae blooms plaguing Green Bay are more than just a nuisance. When that material dies and decays, it burns up massive amounts of oxygen that can lead to "dead zones" – vast areas so low in oxygen that almost nothing can survive.

It starts with the way big bodies of water like Green Bay behave as the summer sun warms their surface. Because warm water weighs less than cold water, such bodies of water have two distinct zones during the summer. The upper, warmer layer can extend about 20 feet below the surface. Then there is a thin transition strip of cooler water before a perpetually frigid zone takes over and stretches all the way to the lake bottom.

Exposed to the atmosphere and its surface-churning winds, the upper layer pulls oxygen out of the air all summer long. But the cool water locked below never gets replenished with oxygen until fall.

That's when, as surface water temperatures cool to match the zone below, the lake loses its layers. Winds are able to mix the water, and the deep zone gets re-oxygenated.

The layered season is typically not a problem in deep lakes where the cold layer is so vast that there is plenty of oxygen within it for the fish and other aquatic life to coast through the summer. But in shallower water bodies, the cold layer is much thinner and therefore prone to run low on oxygen as summer wears on.

The layering of the water is a problem in water bodies plagued by pollution-fueled algae blooms. The algae grows in the oxygen-rich zone near the surface and eventually dies and sinks to the bottom, where microbes decompose it. This burns up precious oxygen, sometimes so much so that a cold zone becomes known as a "dead zone" because it develops oxygen levels so low almost nothing can survive in it.

Peeters' theory was that a dead zone rolled into Green Bay so fast on Aug. 11, 2005, that it chased a species of bottom-dwelling fish — the invasive round goby — to the shore seeking oxygen.

Round Goby Mark Hoffman Native to

Black Sea, Caspian Sea, Sea of Azov and their tributaries in eastern Europe and the Middle East. Threat to Great Lakes

Primarily feeds off fish eggs, which has caused a large drop in mottled sculpin and smallmouth bass populations. When the gobies feed on zebra and quagga mussels, they pass along toxins ingested by the mussels, which causes more damage up the food chain. Discovered

Lake St. Clair, 1990. How widespread

Established in all the Great Lakes and many of their tributaries. Highest populations have been found in Lake Erie, Lake Ontario and Lake Michigan.

Unlike many other fish species, gobies don't have a swim bladder that gives them the buoyancy to help them escape a dead zone by swimming upward into the warm layer and its higher oxygen levels. Instead, the gobies swam sideways in a desperate dash for water that would not suffocate them.

"The cold anoxic water traveling along the bottom actually herded the bottom-dwelling gobies right to shore and pinned them there," Peeters, now deceased, theorized in the email to his bosses.

Anatomy of a disaster

Sue Marcquenski, fish-health specialist for the Wisconsin Department of Natural Resources in Madison, started cutting into Peeters' fish specimens the day after the kill.

She saw no signs of inflammation or infection, though she did notice all the fish were covered in mucus, even their eyes, which can be an indication of pollution-induced stress.

Most telling was the fact their gills were packed with red blood cells, a likely response for fish suffocating in oxygen-depleted waters.

She noted their livers were also cream colored — a potential sign of anemia triggered by a physiological response to rush oxygen-grabbing red blood cells to the gills.

Marcquenski sent an email to Peeters, concurring that a lack of oxygen was the most plausible explanation for the fish beaching themselves. But she thought more information about the chemical makeup of the water in the bay was needed to be confident of the conclusion.

"I believe the Green Bay sewerage agency has several monitoring sites through the bay," she wrote. "Don't know if there is one close to the Bay Shore area, but maybe their data would (be) worth a peek to see if there is support for the hypothesis."

Tracy Valenta, a water resources specialist at the Green Bay Metropolitan Sewerage District, had the data the DNR was looking for. Daily oxygen readings from a monitoring station in lower Green Bay had been lurking in computer files for years.

"We had 20 years worth of continuous monitoring data at that point, maybe more," Valenta says. "I started looking at it and thought — this is really fascinating."

She pulled the oxygen data for the week of the fish kill. The undulating line showing oxygen content near the bottom of the bay plummeted from more than 12 milligrams per liter in the spring to below 1 milligram in the days leading up to the kill.

Anything below 5 milligrams is considered oxygen-depleted. The definition of a dead zone, referred to as "hypoxia" by biologists, is anything below 2 milligrams per liter.

Dead zones had been documented in Green Bay as far back as the 1920s.

A dead zone thrives in Green Bay The phosphorus-driven algae blooms plaguing Green Bay are more than just a nuisance. When that material dies and decays, it burns up massive amounts of oxygen that can lead to "dead zones" – vast areas – so low in oxygen that almost nothing can survive. The problem, driven largely by phosphorus-rich manure seeping into the bay and fueling algae blooms, appears to have gotten worse in recent years. This dead zone was mapped in 2012. The researchers taking the oxygen recordings did not sample the lower bay at that time, or the near shore areas.

But with the Clean Water Act pollution reductions, the bay's problem appeared to have lessened, if not disappeared. When Valenta pored over the numbers stretching back into the mid-1980s, she saw that despite more than $300 million spent on water treatment upgrades and an ongoing $1 billion PCB cleanup in the lower Fox River, the environmentfor fish in the bay appeared to be getting worse.

"It was the call about the gobies that really got this started, that made me dive into the continuous-monitoring data," Valenta says.

"It made us realize that we really need to look at oxygen issues in Green Bay."

Readings taken from a gauge in the lower bay showed the average number of oxygen-poor days — defined as levels below 5 milligrams per liter — was 13.5 per year for the 10 years between 1986 and 1995. That average jumped to 32.4 for the years between 2007 and 2013.

Furthermore, the severity of the oxygen-depleted days has gotten worse, dropping from an average just over 3 milligrams per liter during the 1980s and '90s to just over 2.5 milligrams per liter during the past seven years.

And the average number of dead zone days — oxygen readings of less than 2 milligrams per liter — has jumped similarly, going from 3.5 days per year between 1986 and 1995 to 14.5 days from 2007 to 2013.

The fish die-off in 2005 and a similar event in 2011 started with gusty winds coming from the south that pushed northward the warm, shallow water of the lower bay. When that water moves north, just like skimming your arm across the surface of a bathtub near the hot waterspout to even the tub temperature, it creates a whoosh of cold, oxygen-depleted bottom water headed in the opposite direction.

"It's like a freight train coming down into lower Green Bay of low dissolved-oxygen water," Valenta explains.

"How long could you survive with a plastic bag on your head? Because that is what these poor fish are going through."

How did that cold water become so oxygen-depleted?

An overload of phosphorus. Once this fertilizing mineral makes its way into a water body, it acts like fuel to a flame, supercharging nuisance algae blooms, which burn up oxygen to create dead zones.

Phosphorus off the farms Green Bay and the lower Fox River are suffering from a chronic overdose of phosphorus. There are lots of sources for the nutrient — city sewerage systems, industries, runoff from lawns and streets — but as this chart shows, agriculture is by far the largest contributor. The state has a plan to put the river and Green Bay on a phosphorus diet under the Clean Water Act. This likely will require expensive pollution-reduction investments for cities and industries, but agriculture runoff remains largely beyond regulation under the Clean Water Act. Sources of total phosphorus loading in the lower Fox River basin, in pounds per year Source: Wisconsin Department of Natural Resources

Data provided by the state Department of Natural Resources show that phosphorus levels in parts of Green Bay have been, in most years, far beyond what is considered healthy. The target level for the open waters of Lake Michigan is 0.007 milligrams per liter. In recent years, levels 30 times that amount have been detected in the bay.

Yet the old pollution culprits of heavy industry and human sewage are no longer the primary drivers of the problem; the amount of phosphorus pouring from their pipes into Green Bay is just a fraction of what it was four decades ago.


"The Clean Water Act did what it was supposed to do," says Val Klump, director of the University of Wisconsin-Milwaukee's Great Lakes WATER Institute. "It cracked down on sewerage districts and industry."

Klump, who holds a law degree from Georgetown University and a PhD in marine sciences from the University of North Carolina, notes that the Green Bay sewerage district, now known as NEW Water, has gotten so good at taking phosphorus out of its discharges that it is no longer a major factor in the algae blooms.

"Even if you take their load down to zero, we still have a problem," he says.

The papermakers and other industries have made similar improvements in recent decades.

So what is the problem?

Take a look at Wisconsin's license plate. The answer lies in the farm fields just above the sailboat flying across a blue lake.

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