Watercraft Shoreline Test
This indicator measures the number of single noise-event exceedances caused by motorized watercraft in the shorezone of Lake Tahoe. Single noise event threshold standards are based on the numerical value associated with the maximum measured level in acoustical energy during an event. High noise levels can reduce the public's enjoyment of the natural environment, impact the quality of life for residents, and disturb native wildlife. Single noise event violations in the shorezone can be caused by boats navigating too close to shore within the no-wake zone and loud boat engines outside the no-wake zone. Regional programs such as prohibiting noisy boat engines and enforcing the no-wake zone aim to reduce single noise events in the shorezone of Lake Tahoe.
Status
The average number of documented exceedances per day for motorized watercraft determined by the shoreline test (greater than 75 dBA). This is averaged across all sites.
Source: TRPA shorezone monitoring data.
Evaluation Map
Shoreline Noise Monitoring Locations
2023 Evaluation
- Status
- Somewhat Worse Than Target
- Trend
- Little or No Change
- Confidence
- Moderate
Applicable Standard
N4: The following maximum noise levels are allowed: Watercraft: Shoreline test - 75 Lmax - measured with microphone 5 ft. above water, 2 ft., above curve of shore, dock or platform. Watercraft in Lake, no minimum distance.
Key Points
- The number of noise exceedances along the shoreline has gone up and down with no trends evident since monitoring began.
- The number of noise exceedances is very low compared to the number of boating hours, with an average of less than one noise exceedence every day. Exceedance numbers are higher during years with a higher number watercraft launches.
- The majority of noise violations appear to come from "go-fast / cigarette" boats, with some violations being caused by boats navigating too close to shore within the no-wake zone.
- TRPA patrols the no-wake zone and has created resources to inform boaters of the no wake zone including the Tahoe Boating App which has been installed by over 17,000 users between 2020 and 2023.
- No wake zone enforcement has increased every year since 2019.
- Most noise violations occur at Rubicon Point and Emerald Point.
About the Threshold
- This indicator measures noise generated from motorized watercraft in the shorezone of Lake Tahoe. Residents and visitors are concerned about the declining serenity of their communities and their enjoyment of the outdoors due to excessive noise from sources such as motorized watercraft. Excessive recreational boat noise can also disturb sensitive wildlife. For this reason, TRPA adopted policies and ordinances to reduce noise levels and maintain serenity in Lake Tahoe’s shoreline area, while continuing to afford recreational opportunities.
- Watercraft-generated single-event noise exceedances are driven by the type of watercraft engine and exhaust system and boater behavior (proximity to shore, operating speed, etc.). Shoreline topography, wave slap, and wind can also influence noise levels.
Delivering and Measuring Success
Local and Regional Plans
Monitoring Programs
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Noise - Shorezone
Noise monitors are put out for two weeks during peak boating season (July 4th to Labor Day). Noise monitors automatically record all single noise events that exceed 75 decibels (dB).
Rationale Details
- Somewhat Worse Than Target. The current status was determined using the average number of noise exceedances caused by motorized watercraft during the four-year evaluation period. There was an average of 0.23 daily exceedances at all monitoring sites between 2020-2023. The threshold is zero exceedances, therefore, the status is 23% worse than target and is considered somewhat Worse Than Target. Limited monitoring was conducted in 2021 due to extensive periods of smoke on the lake and lower than normal boating activity.
- Little or No Change. Trend was determined by analyzing the average number of noise exceedances per day at all monitoring sites combined in each year of monitoring. Over this time, there was little to no change in the number of noise exceedances. There are encouraging signs that the changes made to no wake zone education and enforcement following the shoreline plan are having a positive impact. In the two years prior to adoption, an average of .45 exceedances were observed a day, in the five years after that number has dropped to 0.23.
Confidence Details
- High. Standardized protocols were used throughout the monitoring effort and a large data set exists.
- Low. Confidence of trend is determined by the coefficient of determination value (Low. R²=0.024) and t-test significance (Low. p-value=0.63).
- Moderate. If one confidence rating is high and the other is low, the overall confidence rating is moderate.
Additional Figures and Resources
No photos available.
No documents available.