Motorized Watercraft Effects in Aquatic Ecosystems

As the intensity of boat traffic and typical horsepowers increase with demographically-driven(re-)development of lakeshore, we have reason to be concerned about adverse impacts of boat motors on aquatic ecology. Asplund (2000) provides an excellent and understandable 21-page review of relevant studies. Unfortunately, the trends revealed are more than a little disconcerting. Asplund's review deserves wide circulation among lake associations and others concerned with maintaining ecological integrity of our lakes and streams.

As the preceding fihure shows, adverse impacts are not limited to very shallow areas. A 100 HP motor can stir-up phosphorus-laden bottom sediments down to water depths of 18 feet! When the paper this figure is derived from was published in 1991, a 100 HP motor was near at the upper end -- now motors in excess of 200 HP are relatively common even on small lakes.

Prop wash can greatly increase turbidity, re-suspend algae stimulating phosphorus, and disturb critical spawning and nursery habitat for fish and other aquatic animals. Perhaps most critically, prop wash can destroy plant communities effectively "plowing" lake bottoms and opening sediments to invasive species such as Eurasion watermilfoil (EWM).

Want to reduce the likelihood and adverse impacts of EWM on your lake? Consider comprehensive educational campaigns or local ordinances to reduce damage to native plant communities caused by careless (though seldom malicious) powerboaters. That will, of course, be a very tall order since old habits die hard.

One excellent place to start would be to provide signage at accesses discouraging the now almost ubiquitous practice of power-loading (i.e., driving your boat on to the trailer) . Power-loading produces a pronounced scour hole and wide spread sedimentation at just the place where invasive species are most likely to enter a lake. In effect, power-loading is equivalent to putting out a welcome mat for Eurasion watermilfoil and other invasive plants. With spring just around the corner, it is time to think about such things...