There are also many invasive species that are primarily brought in the ballast water of foreign ships, usually from the ocean bordering Northeastern Asia. This water is dumped directly into the Great Lakes, depositing a variety of fresh and salt water fish and invertebrates, most notably the zebra mussel, "Dreissena polymorpha". There are also many plant species that have been transported to the Great Lakes, including purple loosestrife, "Lythrum salicaria" and "Phragmites australis", both of which are considered to be a threat to native hydrophyte wetland plants.