GRAND RAPIDS, Minn. - The first zebra mussel babies, called veligers, were confirmed in Lake Winnibigoshish in 2012.
By 2016 the first adult mussels were spotted.
By 2018 the invasive filter-feeders are everywhere in the lake, located west of Grand Rapids.
"They've just exploded in number in just a couple years. It's amazing. They're on every smooth substrate down there," said Gerry Albert, Lake Winnibigoshish large-lakes fisheries specialist for the Minnesota Department of Natural Resources.
It's one of the fastest infestations of the thumbnail-size mussels from Eurasia, known for their zebra-striped shells, that are marching across Minnesota, mostly spread by anglers and other boaters from lake to lake.
The mussels filter algae and other particles out of the lake wherever they go, and that in turn makes the water more clear. For Big Winnie, the water clarity increase has been rapid and astounding - more than doubling, from 6-7 feet before the mussels arrived to 14 feet and more now.
"We've seen it up to 22 feet," Albert told the News Tribune. "It's gone from a murky lake to a crystal-clear lake overnight."
Tom Neustrom, a longtime Grand Rapids-area fishing guide, agreed.
"I've been fishing Winnie for 35 years and I've never seen it as clear as it was last summer. It's astounding," he said.
Doug Jensen, aquatic invasive species expert for Minnesota Sea Grant, said the Winnibigoshish zebra mussel explosion happened faster than in most lakes they have invaded but was "not unheard of." And he warned people to get used to the ever clearer water.
"Each of those little mussels can filter between one and four liters of water every day," Jensen noted. "They're taking a lot of good food out of the water column and leaving a lot less on the plate for the rest of the food web."
What impact the mussels will have on Winnibigoshish's storied reputation as a walleye fishing legend is unknown. But the big change in the lake's ecosystem, along with other issues in walleye reproduction, was enough for DNR officials to call a special public meeting for March 20 in Grand Rapids. So far, no fishing regulation changes are proposed. And there's no known way to get rid of the zebra mussels.
"We don't have any plan. We just want to share what we know with the average fisherman who uses the lake, maybe talk about where we think things might go ... see what people think," Albert said.
Even before the mussels took hold, DNR experts were seeing some issues with walleyes - namely fewer small fish. It's not clear why the lake's bigger fish are doing well but small fish aren't as numerous, Albert said.
"I don't want to blame zebra mussels for the (walleye) recruitment issue. They are two different things going on once, or maybe multiple things," he said.
Big walleyes are doing well, growing fat and fast on an abundance of perch and shiners.
"We're just not seeing the small fish moving up into the" size anglers want to catch. There have also been fewer male fish showing up in spring to spawn.
Not only are there fewer catchable walleyes, but the newly clear water is apparently making them harder to catch. Walleyes are notorious dark-water feeders, avoiding bright light when possible as they seek their prey. As water clarity increases, so does light penetration, and that makes walleyes scatter to deeper waters, or water with more weeds, where anglers aren't used to fishing.
Neustrom said the lake's walleye fishing has been diminishing for about four years. The problem, he said, is that anglers aren't catching many fish they can keep to eat - walleyes below the protected slot limit between 18 inches to 23 inches long, fish that must be immediately released.
"I think I only fished (Winnibigoshish) four times last year and all we caught were big fish. There's something wrong there where we aren't seeing small fish at all,'' Neustrom said.
Neustrom said it's not yet clear if Winnie's problems are similar to Mille Lacs Lake where an explosion of zebra mussels was accompanied by a declined in walleye fishing - too soon to say what role the mussels may be having on the fish.
Neustrom hopes the DNR considers adjusting the slot limit to allow larger fish to be kept by anglers.
"I think there's an overabundance of biomass out there. Too many big fish," he said. "There's probably some cannibalism going on. Maybe they (DNR) can't solve the problem with regulations. But we need to try something."
Albert noted that zebra mussels don't necessarily mean the end of walleye fishing or even necessarily a major decline. Walleyes continue to thrive in places like Lake Oneida in New York and Lake Erie where zebra mussels virtually cover the bottoms of the lakes. The fish even spawn on top of layers of zebra mussels.
"The research from places where they have had zebra mussels for decades now seems to show that you still get walleye reproduction, but fewer strong year classes," he noted.
Starry stonewort expanding
If there weren't enough new issues facing Winnie there's also a new infestation of Starry Stonewort, an invasive underwater flower that's relatively new to Minnesota but spreading fast.
Starry stonewort, a grass-like species of macroalgae, was first confirmed in Lake Winnibigoshish in 2016 but had already infested the western part of the lake. Now it's moving across the lake to the eastern shore, Albert said.
The weed is apparently growing best near the first major drop-off out from shore, he said.
DNR invasive species experts said the extent of the spread and depth of starry stonewort in Lake Winnibigoshish indicate it has likely been there for several years.
Because the Winnibigoshish infestation is so widespread the DNR said there may be no way to get rid of the weed and instead will focus on preventing it from spreading elsewhere.
The weed, which has burst onto the Minnesota invasive scene with little advance notice, is spread mostly by boaters who unwittingly allow it to hitchhike as they trailer their boats from one lake to another - much like zebra mussels, spiny waterfleas, Eurasian water milfoil and other aquatic invasive species. But because giant Lake Winnibigoshish also is connected to the Mississippi River, DNR officials say they are also checking to see if the invader has moved downstream.
Starry stonewort gets its name from tiny star-shaped blossoms amid a tangle of green foliage. It's a native of Europe and western Asia and was first reported in the U.S. in 1978 along the St. Lawrence River, apparently arriving here in ships' ballast water, according to the U.S. Geological Survey. It's been in Michigan since 1984 and was confirmed in southeastern Wisconsin in 2014 and in Sturgeon Bay of Lake Michigan just last week. The aquatic plant was first confirmed in Minnesota in Lake Koronis near Alexandria in 2015 and has since spread to a dozen lakes and probably more.
Clean, drain, dry
Zebra mussels (and starry stonewort for that matter) can't move on their own, but they move with currents or are moved - usually accidentally - by people. They attach themselves to any smooth surface under water and feed by filtering nutrients out of the water.
Zebra mussels are believed to have moved from their native Eurasia into the Great Lakes in the ballast of oceangoing ships. They first were found in Minnesota in the Duluth harbor in 1989 and then began to explode in numbers in the Twin Ports harbor by 1998. They also have moved north into Minnesota through the Mississippi River system and have been moved by humans into several lakes.
But experts say it's not inevitable they will invade every lake. While more lakes and rivers are seeing invasions of aquatic invasive species, efforts continue to keep the invaders from spreading. So far, the effort appears to be working to at least slow the spread.
Jensen noted only about 1 percent of Minnesota's 11,000 lakes are infested with zebra mussels, just a fraction of what would be infested if people weren't taking precautions.
Boaters, anglers, divers, waterfowl hunters and others who visit infested lakes are urged, and required by law, to prevent moving any water from one lake or river to another. It's also mandatory to empty bilges and livewells and remove any weeds from boat trailers.
The rules mean draining, cleaning and drying all parts of boats that are trailered to different lakes. It also means not moving bait between lakes.
If you go
- Minnesota DNR public meeting on changes in Lake Winnibigosh ecosystem
- March 20, 7-10 p.m.
- Minnesota Interagency Fire Center, 413 SE 13th St., Grand Rapids
- Free and open to the public.