Wisconsin Watersports Coalition

Aquatic Invasive Species (AIS)

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Spread of Aquatic Invasive Species. Wake boats/Ballast Boats are Not the Highest Risk

It’s important to recognize that any boat that remains on a single lake throughout the season does not contribute to the spread of aquatic invasive species (AIS). If the rationale for restricting wake boats is the potential risk posed by trailered boats spreading AIS, then that same rationale must extend to all types of boats.

AIS contamination is a significant concern for all types of watercraft, but wake boats are not uniquely problematic. Even though the internal ballast systems of wake boats are difficult to inspect, all watercraft and trailers can retain water and have areas that are difficult or impossible to sterilize or inspect, thus posing a risk. These areas include sterndrive/outboard engines, including the lower units, bilges, live wells, splash wells, foot wells, and even jets.

The Doll study in Minnesota is one of the more comprehensive studies to look at regarding AIS, focusing on zebra mussels, which involved multiple boat launches. Data on thousands of watercraft was collected over a span of months. Some of the findings include:

AIS was found in all watercraft compartments. While ballast tanks had the highest average, the highest concentration was found in a sterndrive engine.
The study assessed 11,123 boats at boat ramps over a two-month period. Fishing boats comprised 60.5% of the samples taken, runabouts 25.2%, and wake boats only 3.7% (Figure 9 below).
The study also noted that over a two-year period on Minnesota lakes, 865,000 watercraft were inspected. Of those watercraft, 66% were fishing boats. That's over 570,000 fishing boats traveling between lakes in those two years.
In assessing the compartments found on different watercraft and the likelihood of veliger transport, both runabouts and fishing boats were rated as a moderate risk, while the ballast tanks, due to the volume of water, moved the wake boats into the high-risk category (Table 5 below). Note: This risk assessment does not take into account the relative frequency of traversing lakes.
The study's key factors in assessing the risk of transporting veligers are time and temperature. The longer the time between traversing lakes or the higher the temperature exposure, the higher the mortality. Various studies involving AIS have shown that this is generally true for most AIS. Doll identified that the greatest risk is traversing lakes within a 6-hour time period.
Doll referenced MN Statute § 84D.10, which requires the removal of drain plugs and draining of remaining water. However, it's been determined that this method still isn't 100% effective because “residual” water often remains trapped inside the watercraft after all drain plugs are removed. (Montz et al. 2016; Campbell 2016).

The relative risk of spreading invasive species can be effectively evaluated by calculating a Risk Priority Number for various types of watercraft. By considering both the likelihood of an event occurring and the frequency of such events, this method allows for an objective risk assessment across different types of watercraft. The distribution of boat types serves as a useful reference for estimating the frequency of exposure. By assigning risk values—1 for low risk, 2 for medium risk, and 3 for high risk—the relative threat posed by each boat type can be quantified. Accepting the conclusions of Doll’s study, which suggests that wake boats represent a high risk for spreading invasive species and that fishing boats, runabouts, and pontoons represent a medium risk, a risk priority number can be calculated by multiplying the risk value by the frequency of each boat type. This analysis demonstrates that fishing boats are at 11 times higher risk for spreading AIS, an order of magnitude more, than wake boats. Runabouts are 4.5 times higher risk.

However, this analysis is conservative and overestimates the actual risk associated with wake boats. Fishing boats frequently move between lakes, often on the same day, substantially increasing their potential to spread invasive species. In contrast, wake boats rarely travel between multiple lakes in a short time frame, indicating that their frequency of exposure is underestimated. Adjusting the risk value for fishing boats and runabouts to high would result in fishing boats presenting a risk 17 times greater than wake boats.

The data do not support the perception that wake boats pose a unique or disproportionate threat. The risk is more evenly distributed across various watercraft types, with wake boats representing one of the lowest relative threats.

In 2008, Notre Dame conducted a study assessing boating traffic in northern Wisconsin and the Western Upper Peninsula. The study found that most boaters fish in the same small number of lakes. However, about 30% of boaters move among lakes, sometimes visiting multiple lakes in a single day. And boaters who moved between unconnected lakes often (more than once every 5 days) were categorized to be at a greater risk of transmitting AIS (Witzling et al., 2016). In contrast to fishing boats, most wake boats are used primarily on their owner's home lake. Also, while efforts are increasing to inspect and clean boats and lakes to efficiently prevent AIS from spreading, only 56% of boaters and approximately 80% of trained professionals successfully removed all AIS during a controlled study (Angell, 2023).

In response to questions regarding wake boats and AIS prior to the Natural Resource Board meeting in June of 2024, Lt. Kuhn of the Wisconsin DNR wrote, “...AIS were already established in hundreds of inland lakes in Wisconsin prior to the rise in wake boat popularity…To fully understand the impact of wake boats on the spread of AIS, more information is needed,....and the frequency with which wake boats move amongst bodies of water.”

Understanding the overall risk pertaining to AIS exposure comes down to both individual watercraft risk and the frequency of traversing lakes. When discussing AIS with professionals, a maximum allowable amount of retained AIS has never been deemed acceptable, meaning it doesn't matter whether 10 or 200 examples of AIS is present, even one is considered too high. This makes the frequency of traversing lakes an even more significant risk. A wake boat that's labeled high risk due to its ballast tanks but with a very low rate of traversing lakes (3.7%) doesn't pose any greater risk than boats (fishing/runabout) labeled as a moderate risk but have a much higher rate of traversing lakes, even within the same day(85.7% combined; percentages from Doll 2018).

While AIS is a valid concern, comprehensive policies should target all watercraft, and efforts should be directed toward improving sanitization and certification practices rather than focusing solely on wake boats.

The use of Antifreeze:

The use of aniti-freeze for winterizing wake boats is not an indication of the amount of water in a ballast. Antifreeze can be and is used in both outboard and sterndrive engines (any engine that is water cooled) for winterization steps to prevent pockets of water from causing damage. Wake boats require similar precautions and steps.

Figures from Doll, Adam, MS Thesis University of Minnesota, Dec 2018

References:

Doll, Adam (2018) Occurrence and Survival of Zebra Mussel Veliger Larvae in Residual Water Transported by Recreational Watercraft; MS Thesis University of Minnesota

Witzling, L., Shaw, B., & Seiler, D. (2016). Segmenting boaters based on level of transience: Outreach and policy implications for the prevention of aquatic invasive species. Biological Invasions, 18(12), 3635–3646. https://doi.org/10.1007/s10530-016-1254-7

Angell, N. (2023). Cost-effectiveness of aquatic invasive species prevention techniques [University of Minnesota]. https://hdl.handle.net/11299/258841

Campbell, T., Verboomen, T., Montz, G., & Seilheimer, T. (2016). Volume and contents of residual water in recreational watercraft ballast systems. Management of Biological Invasions, 7(3), 281–286. https://doi.org/10.3391/mbi.2016.7.3.07