 Introduced species are also directly affecting the freshwater pearl mussel; the invasion of the zebra mussel ("Dreissena polymorpha"), which has been spread to new locations by being transported on the bottom of boats or in ballast waters, has impacted freshwater pearl mussel populations in all countries it has invaded.The freshwater pearl mussel, which is completely protected in all European countries, has been the focus of a significant amount of conservation efforts.Measures have included the transfer of adult mussels to areas where it had gone extinct, the culture of juvenile mussels, and the release of juvenile trout, which have been infected with glochidia, into small rivers, but mainly the freshwater pearl mussel has benefited from habitat restoration projects in some areas.