Solar ultraviolet (UV) radiation can penetrate the water column of freshwater habitats and harm aquatic organisms. Typically, field measurements of water column UV radiation are conducted with heavy and cumbersome spectroradiometers utilizing underwater spheres. We describe a simple procedure for predicting the penetration of UV radiation through the water column that does not require the transportation and use of spectroradiometers in the field. This procedure involves collecting small water samples from any pond, lake, stream, or river, and then scanning the samples in a laboratory spectrophotometer. The resultant UV transmittance spectra are then used to predict the penetration of biologically harmful solar UV radiation through the water column of freshwater aquatic habitats.