The USGS measured photosynthetically active radiation (PAR, wavelength between 400 and 700 nanometers) at Malheur Lake, Oregon, as vertical profiles and as continuous measurements at a fixed depth, in 2017 and 2018. Malheur Lake is a large, shallow, turbid lake located in southeastern Oregon that fluctuates widely in surface area in response to yearly precipitation and climatic cycles. High suspended-sediment concentrations likely are negatively affecting the survival of aquatic plants. The PAR measurements in this data release were collected to assess PAR attenuation in the lake, and to quantify attenuation as a function of water quality (primarily turbidity). The continuous PAR measurements were collected at 10-minute intervals at fixed locations in the water column in the northeast and southeast sections of the lake. The profile PAR measurements were collected beside the deployed continuous PAR monitors, and the measurements were taken just above and just below the surface of the lake and at semi-regular intervals down to the bottom of the water column.