There are 30 species of non-native vascular plants within Lake Clark National Park and Preserve. Most of the plants are not considered to be highly invasive and problematic. There is an effort to eradicate the common dandelion from Upper Twin Lakes. There are no known species of non-native animals that are free roaming within the unit.
Maine ocean islands provide the only nesting sites for Atlantic puffins in the United States. Eastern Egg Rock in the midcoast region, Seal Island and Matinicus Rock at the mouth of Penobscot Bay, and Machias Seal Island and Petit Manan Island off the downeast coast provide habitat for more than 4,000 puffins each summer.