Boat Motors and Water Quality

 

As Minnesotans, we love cruising along the lakes in our watercraft.  Whether we are heading to our favorite fishing spot, waterskiing, or taking a sunset cruise, not much can top the feeling of taking in the fresh lake air.

 

Yet as the number of motorized boats and size of motors on Minnesota's lakes continues to increase, questions arise about the potential effects these boats have on the lake environment.  In the last 20 years, there has been a 36% increase in the number of registered boats of all types in Minnesota.  Moreover, the number of motorboats between 16 ft and 26 ft in length increased 118%, while the number of motorboats less than 16 feet decreased by 27%.  Average horsepower went from 46.1 to 74.5 from 1987-2001 in a DNR survey of west central Minnesota.  Our boats are becoming larger and faster, which increases the potential to effect water quality.

 

So how do boats affect water quality?  The Wisconsin DNR did a study on the effects of motorized watercraft on aquatic ecosystems.  Boats can affect water quality in a few different aspects.  First, they can add metals and chemicals to the water column.  A certain amount of the fuel that enters into a motor is discharged unburned and ends up in the water.  Two stroke motors can emit 25-30% of their unburned gas and oil mixture into the water.  In contrast, four-stroke motors emit 97% less air and water pollution than old two-stroke motors.  This pollution can affect the pH and dissolved oxygen in the lake, which can influence the type and abundance of fish and wildlife.

 

Text Box: Effective Mixing Depth Effective mixing depth is the maximum depth at which the engine stirs up the water and, in turn, the lake bottom sediment. The importance of these findings is that power boating in shallow areas on lakes is likely to stir up bottom sediments, decreasing water clarity and releasing nutrients from the lake bottom, which can feed algae blooms. Effective Mixing Depth by Engine Size Horsepower Mixing Depth 10 6 feet 28 10 feet 50 15 feet 100 18 feet Source: Lakeline, December 1991 Another main impact by motors is churning up the lake bottom in shallow areas.  This action stirs up the lake sediment, re-suspending nutrients (phosphorus) that are at the lake's bottom. When these nutrients reach the surface of the water where the algae are, they can feed algae and cause and algal bloom. This stirring can also decrease the water clarity because of additional particles suspended in the water column.

 

So what can you do to protect your lake?  1) Establish no-wake zones in shallow areas with waterfowl nesting and bulrush stands.  "Slow no wake" means operation of a watercraft at the slowest possible speed necessary to maintain steerage, but in no case greater than 5 miles per hour.  2) Educate lake users to avoid sensitive areas and drive slowly through shallow areas.  3) Upgrade your boat motor from an old two-stroke engine to a four-stroke engine.  Four-stroke engines use fuel more efficiently, produce cleaner exhaust, and run more quietly than traditional two-stroke engines.

 

To reduce your impact while boating, there are other easy changes in behavior we can all practice.  1) Keep your boat property trimmed – an engine in the water makes much less noise and creates less wake; 2) keep your engine well-tuned so that it runs more efficiently, pollutes less and is quieter; 3) be respectful to wildlife and loons, keeping a distance of at least 200 feet away at all times; 4) consider the size of your boat and motor when choosing a lake for recreation – smaller lakes are not appropriate for large boats or engines; 5) remember that swimmers, canoeists, kayakers, sailboats and other non-motorized users always have the right-of-way.

 

To read more about the Wisconsin DNR boating impact study visit: http://dnr.wi.gov/org/water/fhp/papers/lakes.pdf.

 

Enjoy the lakes!

 

Moriya Rufer is the Lakes Monitoring Program Coordinator for RMB Environmental Laboratories in Detroit Lakes, 218-846-1465, lakes.rmbel@eot.com.