Water-leaving radiance (L w), or remote sensing reflectance (R rs), is a fundamental parameter of water color remote sensing. However, obtaining accurate and precise measurements of L w is quite challenging. This study is intended to illustrate the design and implementation of a novel floating optical buoy (FOBY) to measure L w directly in the field based on the skylight-blocked approach (SBA). To assess the performance of FOBY, an experiment was conducted in Honghu Lake, China, a typical shallow turbid lake. FOBY-derived R rs can characterize the spectral features of different water types including water with kelp as substrate, relatively high chlorophyll-a contents, and high amounts of suspended sediment (SS). FOBY-derived R rs is superior to that from a portable spectroradiometer (PSR 3500+, Spectral Evolution Inc.) based on the conventional above-surface approach (ASA) in terms of data quality and stability. FOBY measurements had a quality assurance score (QAS) of 0.98 and a mean coefficient of variation (CV) of 3.6-7.0%, while the mean CV for PSR measurements is more than 2 times larger than that of FOBY in the visible domain. The measurement uncertainties may result from self-shading, sensor tilt, and the immersed depth of the cone (IDC), which deserve further investigations. In the future, long-term continuous floating observations of different aquatic environments can be conducted using the instrument with well-refined data quality control.