Boat effects on lake water clarity and the efficacy of a no-wake zone policy

Abstract

Boating activity in shallow waters of lakes can lead to sediment resuspension and potential nutrient release, affecting water quality parameters. No-wake zones, to minimize boating-induced effects, are often defined based on distance from shore. This study assessed the effects of boating on shallow waters and the efficacy of an existing no-wake zone policy in a midsize lake. Two experiments were conducted: (1) Turbidity and pressure data were collected along a broad shallow shelf on the southern shore of Lake Tahoe in the summer of 2019 and (2) turbidity and pressure observations were conducted while boats traveled at speeds between 8 kmh−1 (5 mph) and 40 kmh−1 over a water depth of ≈ 2.5 m. Results showed that boat-induced sediment resuspension occurred at speeds exceeding 8 kmh−1, with turbidity increases of up to ∼7 NTU. Boat-induced filtered pressure signal was a maximum of 40% of the total daily wave activity, with peaks observed between 10:00 and 12:00. Nevertheless, during the summer and fall of 2019, winds were the dominant driver of sediment resuspension, contributing around 80% of the total wavefield. An evaluation of the current no-wake zone policy at Lake Tahoe suggested that an 8 kmh−1 (5 mph) speed limit is suitable for preventing wake effects. However, the policy falls short in preventing sediment resuspension in the northwestern and southern shores of Lake Tahoe. This calls for the consideration of multiple variables, such as lakebed sediment type and water depth, when defining no-wake zone policies to effectively mitigate boating-induced effects.