This study tested different combinations of rice straw and water hyacinth (an invasive aquatic weed) as growing substrates for oyster mushrooms in Nepal. Rice straw alone produced the best mushroom yield and profit. While water hyacinth alone is not suitable as a substrate, mixing it with rice straw at a 2:1 ratio could reduce costs while helping control this problematic weed. This research provides farmers with practical guidance on sustainable mushroom cultivation methods.