In aquatic ecosystems, the UV and visible radiation environment is strongly influenced by variation in the chemical and physical parameters of the ecosystems. In shallow lakes, highly heterogeneous water characteristics produce a wide variety of optical environments. Such ecosystems require analysis approaches that consider a potential variability. In this study, 77 stations were used to characterize the optical properties of a shallow lake (open water surface 54 km²). The vertical attenuation of solar radiation at 305, 313, 320 and 340 nm and at photosynthetically active radiation was measured during the seasonal cycle. Dissolved organic matter (DOM), turbidity, fluorescence, pH, temperature, conductance and dissolved oxygen were simultaneously measured. The spatial variation of the extinction spectra of the dissolved fraction at each sampling station was also measured and analyzed between 270 and 400 nm. The spatial heterogeneity of the lake was examined by determining the distributions of the attenuation coefficients and biooptical parameters at high spatial resolution and describing the distributions in a series of maps. The methodology permitted a quantitative description of the interaction between solar radiation and aquatic ecosystems as well as a spatial classification of the dominating processes within the lake. This included the determination of the role played by DOM loading and changing chemical properties within the lake optical environment.