Aquatic invasive species in the Boundary Waters

Art & Science By Meg Duhr, Minnesota Aquatic Invasive Species Research Center

When you go out to paddle your canoe, are you helping to spread invasive species?

Often when we think about aquatic invasive species (AIS), motorboaters and busy lakes near densely populated areas come to mind. 

And for good reason. 

Research into several decades of invasion patterns show us that the majority of AIS spread throughout Minnesota lakes via motorized watercraft. They come in a bewildering array of makes and models with tons of places for AIS to hide. Motorized watercraft can be difficult to clean; and with a trailer, boaters can bring them from one lake to another in a short period of time. 

On the other hand, water travel within the Boundary Waters is slower, cleaner, and simpler. It’s a method of travel that has helped maintain functioning lake ecosystems and the fantastic recreation and fishing opportunities we love about the Boundary Waters. 

However, that doesn’t mean that AIS aren’t a concern in the Boundary Waters. 

Some species have made a perch right at the doorstep of the BWCAW. For instance, zebra mussels are established and reproducing in Rainy Lake. And other high impact species like spiny water flea and rusty crayfish have infested popular entry lakes and even several lakes deep in the wilderness. 

Even in the best of circumstances, controlling these species is complex and expensive, involving mechanical devices, pesticides, and significant people power. In the wilderness, managing these populations and reducing their impacts would be monumentally more difficult.

This heightens the stakes. 

Because of this, padders have an important role to play in preventing further spread of these species and ensuring that no new species are introduced.

Photo courtesy of Minnesota Aquatic Invasive Species Research Center

The Spiny Water Flea in Canoe Country 

Why should we care about invasive species in the Boundary Waters? 

Simply put, aquatic invasive species degrade and destabilize lake ecosystems through multiple mechanisms, reproducing at explosive rates, consuming resources that native species depend on, or changing the habitat conditions that support native plants, fish, and wildlife. 

The spiny water flea is one such invasive species already present in the BWCA that provides an excellent case study on the negative impacts of AIS and what we can do to prevent them from spreading into even more lakes inside the wilderness.

About the size of a grain of rice and semi-transparent with a long, barbed tail spine, spiny water fleas are tiny crustacean zooplankton (not insects!) that are barely visible to the naked eye. 

Though they seem small to us, compared to our native zooplankton species, spiny water fleas are massive — about twenty times as large as native water fleas. 

They are also voracious predators that consume vast amounts of native zooplankton. 

This is a major concern in Minnesota lakes because zooplankton are a critical part of the diet of many fish species when they’re in their early life stages. 

Another worry is their barbed tail spine. This makes them nearly inedible to the fish species that consume zooplankton as prey. With explosive reproductive rates, virtually no pressure from predators, and a major competitive advantage in their size and feeding habits, spiny water fleas can quickly become the dominant zooplankton in a lake. This can have a cascade of impacts up and down that lake’s food web. 

And if you like to fish in the Boundary Waters, you should be especially concerned. 

Invasive Species Harm Fish

Researchers have found that walleye in their first year of life grow more slowly in spiny water flea-infested lakes, finishing their first summer 12-14% smaller than baby walleye in spiny-free lakes. This means that these young fish are less robust and less likely to survive their first winter, eventually leading to declines in the local population.

Spiny water fleas are typically spread between lakes through residual water (leftover water in partially drained gear and boats) and contaminated fishing gear. 

The barbed tail spine that gives spinys a competitive edge also allows them to latch onto fishing line and tackle. Surface trolled fishing lines and downrigger lines are the riskiest types of gear because the fishing line is moving horizontally through the water column, entangling spiny upon spiny on the line and sometimes resulting in gelatinous-looking clumps containing dozens to hundreds of individuals. 

Photo courtesy of Minnesota Aquatic Invasive Species Research Center

Prevent the Spread of Invasive Species

If you put out a trolling line while you’re paddling or use tackle like a Dipsy Diver, it’s imperative to wipe down your line, fishing pole eyelets, and tackle with a quick-drying cloth before moving between lakes. This helps ensure that any spiny water fleas potentially caught on your gear don’t hitch a ride to a new lake. 

A puddle at the bottom of your canoe is plenty of water for a spiny water flea to survive in. Making sure your canoe and any lake water holding containers like bait buckets are fully drained and wiped out is also important for preventing the spread. 

As a bonus, this means you won’t have that annoying shower of lake water down the back of your neck while portaging! 

Be sure to wring out and stow this cloth where it can dry—any spinys left on the cloth will quickly perish in dry, sunny conditions, but if your cleaning cloth stays wet and ends up crammed under a canoe pack, they could survive and spread to another lake. 

Photo courtesy of Minnesota Aquatic Invasive Species Research Center

Cleaning your gear and ensuring you’re not transporting lake water during portages eliminates much of the risk for spiny water fleas and other AIS such as zebra mussels. To prevent all AIS that threaten the Boundary Waters, there are just a few other easy steps to build into your paddling routine.

Steps to Protect Clean Water and the Boundary Waters

  • Remove any trailing vegetation that may have gotten caught on your canoe, fishing net, or footwear. Many types of invasive aquatic plants can spread by fragments, so it’s important to remove any-and-all plant material before entering a new lake.
  • Never discard baitfish into the water. Multiple fish pathogens have been found in Minnesota’s baitfish supply. Angler release is the riskiest behavior associated with this threat and it is already illegal to dispose of live baitfish in the water. Bury any used baitfish inland as you would other fish carcasses: At least 200 feet inland, away from portages or campsites and covered with leaf litter or rocks. Used baitwater can harbor AIS and pathogens and should be poured out on dry ground at least 200 feet from a lake or stream.
  • Never discard nightcrawlers on land. If you use nightcrawlers for bait, all leftovers should be packed out and put in the trash. There are no earthworms native to North America, and invasive jumping worms would be particularly catastrophic for northern forests because they rapidly and dramatically alter the soil structure and nutrient availability of the forest floor in ways that hurt understory plants, limit tree regeneration, and increase erosion. While jumping worms are unlikely to be used intentionally for live bait, the risk of contamination means that this type of bait should never be dumped onto the ground.
Photo courtesy of Minnesota Aquatic Invasive Species Research Center

Other tips to stop aquatic hitchhikers:

  • Consider adding a Swedish dish cloth to your gear list. These ultra-light cloths are a combination of a sponge and a washcloth and they are ideal for wiping out canoes, cleaning fishing gear, and soaking up residual water. They dry very quickly and don’t have looped fibers (like many other cotton and synthetic cloths) which can catch spiny water flea tail spines.
  • Using artificial bait is the safest choice in terms of AIS prevention and saves you the hassle of maintaining, transporting, and disposing of live bait. Making this switch also eliminates the need for changing out bait water between lakes.

As aquatic invasive species get closer and closer to the Boundary Waters and those already inside the wilderness encounter an increasing number of visitors, being careful about invasive species prevention takes on greater urgency. 

We are all familiar with recent news stories about pandemic-era pressures on the Boundary Waters, with many new visitors exhibiting less-than-respectful wilderness ethics. The impacts of litter, disrupted solitude, or cut trees near campsites should not be discounted, but we need to remember that these impacts are temporary, contained, and for the most part, fixable. 

However, when new invasive species are introduced to an area, particularly to a remote location, they are likely there to stay. Once established, the population will spread within a lake unabated and its impacts will only worsen over time. 

But it doesn’t have to be this way.

With minimal options for controlling the AIS that threaten the Boundary Waters we must remember that prevention is our best tool. The steps outlined here may add another two minutes to your portage but protecting the biodiversity and scenic beauty in one of our last best places on Earth is well worth it.

Meg Duhr is the Research Outreach Specialist for the Minnesota Aquatic Invasive Species Research Center where she works to translate AIS research into action and serves as a bridge between researchers and managers, supporting decision-making and implementation of research-informed management. Website:

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