The coming of cooler weather in the northern United States means an end to the boating and motorcycling season for many. As most of us prepare to store our boats or motorcycles for the grueling winter, it's critically important that we do so properly, or face thousands of dollars in engine repairs come springtime.

Chiefly important in preparing for winter is managing the potential for engine damage from the federally mandated ethanol blend in the nation's gasoline supply.

Ethanol in gasoline can damage marine and motorcycle engines. Specifically, ethanol blended gasoline such as E10 (10 percent ethanol by volume) or higher, combined with moisture and a long storage period, can lead to "phase separation" of the fuel, which leaves a corrosive water-soaked ethanol mixture at the bottom of the gas tank.

Without preventive maintenance, this mixture can cause significant damage. In fact, half of the respondents of a recent Boat Owners Association of the United States survey reported that they have had to replace or repair their boat engine or fuel system parts due to suspected ethanol-related damage, costing an average $1,000 for repairs.

To prevent ethanol problems over the winter, boats with built-in gas tanks should have fuel stabilizer added and the tank left nearly full to minimize the volume of moist air that can be drawn in through the tank's external vent. It's the inevitable daily temperature fluctuations that can draw in this humidity and lead to phase separation. E10 fuel remaining in small portable gas tanks (and not pre-mixed with 2-stroke engine oil) should be poured into your car's gas tank and used quickly.

For motorcycles, store them with a full tank and fuel stabilizer, as described above, or drain the tank and fuel system completely to remove all traces of the fuel because ethanol can cause damage if it's left to sit in the tank throughout the winter.

So how did ethanol get into our gas? Signed into law in 2005 and expanded in 2007, the Renewable Fuel Standard requires an increasing amount of biofuels such as corn ethanol to be blended into the gasoline supply. Enacted with the best of intentions, the RFS - and specifically the ethanol mandate - has failed to achieve promised consumer and environmental benefits.

In addition to winter storage and engine repair concerns, ethanol-blended fuel is actually worse for the air and water. According to research from the University of Tennessee, ethanol's "clean alternative" record is "highly questionable," as corn ethanol specifically has been shown to increase ground level ozone. And the 2014 federal National Climate Assessment reported that ethanol production can require 220 times more water than gasoline.

Motorcyclists and boaters know that pure gasoline - or E0 - is the best fuel choice for their engines. According to a BoatU.S. survey, 91 percent prefer non-ethanol fuel for their boats - but only about half found it available. An American Motorcyclist Association-commissioned poll found 78 percent of voters have "very serious concerns about E15 use" and 70 percent oppose increasing ethanol in gasoline.

But the Environmental Protection Agency ignores the public's concerns and continues to increase the amount of ethanol required to be blended in the nation's gas. Even though it's illegal to use E15 (15 percent ethanol by volume) in marine engines, snowmobiles, motorcycles, lawnmowers and any vehicle made before 2001, E15 can now be found in 24 states. And using E15 in many vehicles on the road today will void manufacturer warranties, too.

With a recent $100 million USDA grant to subsidize installation of blender pumps at gas stations throughout the country, access to ethanol-free gas may soon be more difficult, leading to more cases of inadvertent misfueling and engine damage.

Thankfully, Congress is considering bipartisan legislation to repeal the ethanol mandate. As we enter the winter season, boaters and motorcyclists must take the proper steps to protect their equipment. The question remains, will Congress protect consumers and the environment by eliminating the ethanol mandate?

Margaret Podlich is president of the Boat Owners Association of the U.S., the nation's largest recreational boat owners group; Rob Dingman is president of the American Motorcyclist Association, its largest motorcycling organization.