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Noise Pollution in Ears of Beholder

graph showing the volume of different lake sounds

Comparing Lake Sounds

Personal watercraft (Jet Skis) are causing controversy in Minnesota. A state legislative committee passed a bill in February that would prohibit the use of personal watercraft on lakes of 200 acres or smaller. The bill was defeated in the Minnesota House of Representatives, but it brought the issue to a head in the minds of many Minnesotans. A revised bill later became a law that goes into effect June 1. Under the new law, personal watercraft operation would be permitted only between 9:30 a.m. and one hour before sunset. It also enlarges the no-wake zone, making it illegal to operate at full speed within 150 feet of shoreline.

Glenn Kreag, Minnesota Sea Grant Tourism and Recreation Educator, provided factual testimony earlier this year to the Minnesota House Environment and Natural Resources Committee regarding sound levels on lakes. You might be interested in what he discovered.

“In my search for information, I found that personal watercraft are an issue world-wide, from Great Britain to New Zealand,” Kreag said. “The most credible effort I was able to find that addressed the noise issue was conducted in Rhode Island in 1992.”

This research, which measured noise from motorized watercraft on a 580-acre natural lake called Watchaug Pond, was conducted by Kenneth Wagner, professor and water resource manager with ENSR, an international engineering consulting corporation. The lake is used for a variety of activities including fishing, sailing, bird watching, water skiing, and personal watercraft.

Sound is measured in decibels on a logarithmic scale, the same way earthquakes are measured. For instance, an increase of 10 decibels means that a sound is ten times louder. An increase of 20 decibels means that a sound is 100 times louder.

One important factor about how people perceive sound is how it varies. “A constant sound was found less bothersome than a sound that fluctuates in tone, volume, or frequency,” Kreag said.

The graph with this story indicates Wagner's findings. The range of decibel levels are charted to match how sound is perceived by the listener.

  • First column: A still, quiet evening on the lake produced a reading of about 40 decibels. The wind was still and there was no obvious human activity.

  • Second column: Daytime background sound levels at busy beach areas ranged from 50-60 decibels, with peaks of 70.

  • Third column: An outboard motor boat operator experiences sound levels ranging from 80-100 decibels. Research suggests that sound is perceived as "noisy" when it reaches 75 decibels. This varies somewhat from person to person.

  • Fourth column: A personal watercraft operator experiences sound levels of 85-105 decibels. Earplugs are recommended by the American Hospital Association when sound surpasses this level.

  • Fifth column: For reference, the sound level of a chainsaw is shown, which ranges from 100-110 decibels. At 120 decibels, people's ears begin to hurt and there is high risk of permanent auditory damage.

By Marie Zhuikov
June 1998

Return to June 1998 Seiche

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