Dead Zone Found in Green Bay

Scientists have found a dead zone in Green Bay, and the news sounds just as bad as it actually is.

It’s an area with very little oxygen, where it’s hard for fish and other aquatic life to survive. It runs from Dyckesville to Sturgeon Bay, and Tracy Valenta said it’s gotten worse.

“There’s been an increase,” she said. “That means that we need to really look at what’s happening in the bay a little more closely, as far as oxygen levels.”

A dead zone, known as “hypoxia” in the science community, happens when too many nutrients get into the water. Those nutrients, which typically stem from human activities such as fertilizer use or sewage runoff, cause phytoplankton (tiny plant-like organisms), to grow. Zooplankton (tiny animals) eat the phytoplankton, and as they die they sink to the bottom of the bay. Then bacteria feast on the dead zooplankton and use up the water’s oxygen, making it hard for anything else to survive.

Things such as wind direction and temperature can affect oxygen levels, too.

Valenta, a water resources specialist with the Green Bay Metropolitan Sewerage District, has been studying water quality in Green Bay since 2000. During a presentation for the Alliance for the Great Lakes, she said data dating back to 1986 has shown a big increase in the number of days with low oxygen in the bay. Back in 1990 there were four days in Green Bay with low oxygen. In 2011 there were 43.

“As you can imagine, this is putting a lot of stress on the ecosystem itself,” Valenta said.

Valenta said the low oxygen has likely caused the decline of the local burrowing mayfly populations, an insect often used to track ecosystem health. Populations of the bugs haven’t been seen in many numbers since the 1950s, and even then weren’t as plentiful as the early 1900s.

“It’s not that we don’t have good sediment or the right kind of sediment, it’s just that they can’t live when oxygen levels are as low as they are,” Valenta said. “We have good fisheries, but can you imagine the fisheries we would have if the giant mayfly were in Green Bay?”

Valenta said most of the nutrients dumped in the bay come from the Fox River, with a mix of agriculture, residential and industrial uses. Fox River sediments and nutrients end up moving to Sturgeon Bay and depositing right below Chambers Island. Most of the nutrients that get dumped into the bay never make their way into greater Lake Michigan.

“Water quality is an issue for you guys up there [in Door County],” she said. “The water quality is no better up where I sample off of Sturgeon Bay than it is in lower Green Bay, for the most part. Clean water is an issue that’s facing all of us here, and I really think that hypoxia is something to be taken seriously. It’s the result of a larger issue at hand – it’s nutrient overloading to the Green Bay system from the Fox River.”

Avoiding fertilizer use, picking up after animals, cleaning storm sewer gutters and leaving wild, natural plants along the shoreline helps filter nutrients out of water running into the bay, but Valenta said big changes will have to come from the Fox River valley in order to combat the growing dead zone. New Water, part of the Green Bay Metropolitan Sewage District, will be working with the area’s agriculture industry and municipalities to try and keep nutrients and sediment from dumping into the river and the bay.

But no matter where the nutrients come from, the dead zone is a regional problem. It can affect Door County’s tourism industry, fishing industry and entire ecosystem.

“How much would people pay to have blue water, better water, cleaner water?” Valenta said. “That’s what it comes down to. The water is polluted and it doesn’t look good, and people don’t like to swim in green, algal-laden water.”