Some of the least-wanted AIS in Pennsylvania are European ruffe, sea lamprey, hydrilla, spiny water flea, purple loosestrife, Eurasian watermilfoil, Asian clam, and red-eared slider (turtle). In 2004, Northern snakehead were first found in Pennsylvania waters.

It's not always "foreign invaders" that are the problem. White perch and flathead catfish are other examples of species that have turned up where they don't belong. While native to some PA watersheds, they have been introduced to other areas.

• Biodiversity -- The variety of species, their genetic makeup, and the natural communities in which they occur.
• Introduced species -- A species living outside of its natural geographic range. Can be deliberately or accidentally introduced or brought into the new ecosystem. Also called exotic, non-native, nuisance or invasive species.
• Invasive -- Spreading or taking over. Invasive species often take over or dominate a habitat.
• Native -- An animal or plant originating in a region or geographic range. For example, brook trout are native to Pennsylvania.

• When retrieving your boat for the day, check the boat, motor and trailer for weeds and other things "tagging along."
• Wash your boat's hull with hot water or with a high-pressure spray.
• Drain livewells, bilges and other compartments.
• Drain all standing water from your boat.
• Don't dump leftover bait into the water you're fishing, unless you collected the bait there.