Chroodactylon ornatum is an epiphytic red alga occurring in fresh, brackish, and marine waters, with a nearly cosmopolitan distribution in coastal marine waters and a more local distribution in fresh waters. It grows as branched pseudo-filaments, each with single or multiple series of cells embedded in mucilaginous material, 1-10 mm long, forming pale blue to gray-green tufts, goring on other algae, and vascular macrophytes, including Eelgrass. In 1964, it was first discovered in Lake Erie, and later found in Lakes Ontario and Huron. Since this alga had not been found in the lower St. Lawrence River, it was probably introduced in ballast water, In the northeast Pacific, it had only been reported from southern California, until 1998, when it was found growing on oyster floats in Tatilek, Alaska, om Prince William Sound. Hull fouling, ballast water, and Pacific Oyster transplants.