Fewer Impacts At 10-Feet Or Deeper


Deb Patterson

Studies of the effects of motorized watercraft on the aquatic ecosystems by numerous experts in the field have been conducted and written as early as 1976. A majority of the studies were published in the 1990s.

Timothy Asplund, Wisconsin Department of Natural Resources, Bureau of Integrated Science Services and University of Wisconsin — Madison, Water Chemistry Program, published an 21-page study in March 2000.

Asplund stated there are a number of reasons why boats and boat activity are an important issue, while he noted in Wisconsin the number of boats registered increased by 87 percent since the 1960s, the size of boats also increased by 40 percent. “Along with the bigger boats have come bigger engines.”

The study notes sediment resuspension, water pollution, disturbance of fish and wildlife, destruction of aquatic plants, shoreline erosion are major concerns. These studies have also shown boats do have an affect on water clarity and can be a source of nutrients and algal growth in aquatic ecosystems. Shallow lakes, shallow parts of lakes and channels connecting lakes are the most susceptible to impacts. Few impacts have been noted at depths greater than 10 feet.

The summary of the study notes the effects of boats on aquatic systems are complex and depend on numerous factors. General observations show the physical effects of propeller, waves and turbulence appear to be more of an issue than engine fuel discharge.

Water clarity, aquatic plant disturbance and shoreline erosion are serious issues which can be exacerbated by boat traffic. Second, most of the impacts of boats are felt most directly in shallow waters (less than 10 feet) … third, these effects can have repercussions for other features of the aquatic ecosystem, including the fish community, wildlife use and nutrient status.

These observations all emphasize that the most important area of a lake .. protect is the shallow-water, near-shore habitat or littoral zone. Boats that operate in deep waters with large surface areas are not likely to be impacting the acquatic ecosystem.

Most of the studies have suggested no-wake zones, restricted areas as well as enforcement and education. Many of the environmental problems associated with boat activity could be resolved with better enforcement of existing ordinances or regulations and promoting awareness among boaters, according to Asplund.

“Slow-no-wake rules are often ignored or misunderstood such that impacts to sediments, aquatic plants and shorelines occur even in no-wake zones .. Informing recreators about the value of plants, littoral zones and natural shorelines and how their activities may affect the aquatic ecosystem. If people understand that their activities may be hurting the ecosystem, they may be willing to confine their activities to more appropriate places.”

A study by David Hill and Michele Beachler, civil and environmental engineering Penn State University, concluded near-plane operating speeds are by far the worst with speed limits often inadvertently placing boats rate at these speeds. The study investigated the mechanism of bottom stirring by recreational watercraft through a combination of field experiementation and mathematical modeling.

The study on resuspension of bottom sediments by recreational watercraft, conducted through an experimental and theorectical study of the hydrodymnamic impacts of recreational watercraft in shallow waterbodies .. “the experiments confirm, that this ability is a strong function of boat speed and water depth .. the results of this study demonstrate that boats operating at high speed have no greater impact on the lake bed than boats traveling at idle speeds. The greatest impact is seen when boats are traveling at “near-plane” speeds. This critical speed is a function of the boat size and water depth.”

Posted in Critical Issues

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