None of us would dream of polluting our lake with phosphates, right? Unfortunately, that is exactly what we’re doing when we run our boats at full throttle in water less than 10 feet deep.

Jim Brakken, Wisconsin Association of Lakes Director Emeritus


We live near a shallow channel between two lakes.  It’s common to see boaters zoom up to the channel, then, to protect their prop, throttle way down as they proceed toward the next lake.  Minutes later, they zoom out of the channel, and, slowly, the churned up water between our lakes begins to settle down once again . . . ‘til the next boat comes through.  This is a common scene on our lake and many others across the north.

Thanks to shallow lake education efforts in recent years, however, many boaters are now becoming aware of the damage that can be done not just to our props, but to our lakes.  Most of us now understand the need for slow-no-wake zones.  Because we care about our lakes, most of us take it easy in the channels and shallow flats.  That’s the good news!

Here’s the bad: The damage done by motorized boats goes well beyond the channels and shallows.  Recent research shows that our props can easily disturb the water down to 10 feet.  The wake behind our boat does far more damage than we see.

An interesting study was done on several small, shallow Florida lakes [Yousef, U of Central Florida].  Fishing boats with outboard motors were run around the lake for 2 hours to simulate summer traffic.  The disturbed sediments clouded the water slightly, not unlike many of our northern lakes on a summer afternoon.  Readings were taken for both turbidity and phosphorus after the mixing was stopped. The turbid water began to clear immediately and was back to its original state in 26 hours. The phosphorus, however, cleared more slowly and, after 50 hours, had not returned to normal level. Nutrients normally settled out had been brought back into play by the stirring action of the outboard. And it took over twice as long for the nutrients to settle out again than it did for the water to clear.  Research done in northern Wisconsin by limnologist Tim Asplund, bears this out, too.

We’ve all heard about the hazards of phosphorus. To protect our lakes, many of us make it a point to avoid high phosphate laundry detergents and other products.  Many of the phosphorus based soaps sold just a few years ago are now prohibited. None of us would dream of polluting our lake with phosphates, right? Unfortunately, however, that is exactly what we’re doing when we run our boats at full throttle in water less than 10 feet deep.  Although we don’t see the damage, it’s there.  We are feeding microscopic organisms that can store up to 10 times their normal content of phosphorus.  We are fostering the growth of algae, bacteria and unwanted aquatic plants.  We are altering the ecology of the lake.

The problem is greatly increased as the engine size increases.  Although power boating, water skiing and similar aggressive boating are the worst culprits, all motors have the potential of increasing available phosphorus in the lake for 50 hours or more.  The problem is also greatly increased when the number of boats is increased.  It doesn’t take long for a bunch of boats to thoroughly churn up a lake, providing excessive, unneeded nutrition for unwanted plants and organisms.

What can we do? We can begin with our local lake management organizations. These citizen groups have the ability to educate members and visitors to the lake.  Good lake management should include slow no wake rules in shallow waters. Lake organizations are in a position to encourage boaters to travel at slow-no-wake over weed beds, within 200 feet of shore and in all shallow water. They can also distribute information encouraging aggressive boaters to limit jackrabbit starts and water skiing to deep water only.

Youngsters in our lake families should be guided toward non-aggressive water sports, when possible.  Canoes, sculls, sailboats and kayaks pose no problem to our lakes or environment or health.

Next, we can encourage our town and county governments to place restrictions on aggressive boating behavior on our small lakes and sensitive water bodies.  WAL has strengthened the ability of our local governments to take such actions.

High speed boating and related aggressive water sports over weedbeds and other shallow waters can cause significant increases in aquatic nutrients. The resulting algae and undesirable vegetation can have far reaching effects that could greatly diminish the quality of our lakes.  Individuals and our local lake management organizations can provide information, advocate responsible boating, encourage local government action and contribute to the health and well being of our waters.  Throttle back.  It’s good for the lake!