AbstractAquashade is a dye that is used to control the growth of underwater weeds by reducing light penetration through water. We applied four, monthly applications of 1 μL/L Aquashade to three Channel Catfish Ictalurus punctatus ponds during the summer growing season to determine its effects on water quality and incidence of off‐flavor in catfish. Three ponds were untreated controls. Dye treatments had no effect on nitrite or total ammonia concentrations, hours of supplemental aeration, phytoplankton standing crops, or fish production. Cyanobacteria that are known to produce odorous metabolites were found in all of the ponds at some time during the study. On the sampling date immediately before fish harvest, two ponds in each treatment contained populations of the odor‐producing cyanobacterium, Planktothrix perornata and contained fish that would not be acceptable for processing because of musty off‐flavors. The mechanism of action of the dye—reducing water‐column penetration of light in wavelengths of ~600–650 nm—will have little effect on odor‐producing species of cyanobacteria because those species have physiological adaptations (nonchlorophyll accessory pigments and the ability to regulate their position in the water column), which allow them to thrive in low‐light environments.