A chemical compound called Geosmin is responsible for the earthy smell. The fish could be feeding on decomposing matter. The soil in waterbody in which the fish is found acts as an important element. Clay and loam soils are likely to produce muddy taste. The clay particles suspended in the water absorbs the geosmin and easily passed through the gills of the fish. Trouts and some bottom feeders like tilapia is found to have this odor.