Lampreys are one of the two jawless vertebrate groups in Agnatha. The adult's life is shorter than the larval stage which is known as "ammocoete". They are either in parasitic forms or non-parasitic forms. Parasitic adults attach to other species, rely on the blood or flesh of the hosts, and non-parasitic adults die after spawning. There is little historical data on lampreys because ammocoetes are filter feeders who are in the sediment, and captures of adults were all by chance. The objectives I achieved in this study were included: 1) Compiled all existing PA historical data (prior to 1990s) of lampreys and created database and distribution maps for each species; 2) Sampled historical sites for native lampreys in 2011 by using backpack designed for ammocoetes, documented changes in lamprey communities at the watershed scale; 3) Conducted substrate sampling at sites where ammocoetes were present, analyzed substrate size preferred by ammocoetes; 4) Identified collections to species, compared the current data and historical data to see the presence and absence of native lamprey species and value the changes of distributions. In Pennsylvania, 7 species were found historically. They are Lampetra aepyptera, Lampetra appendix, Ichthyomyzon bdellium, Ichthyomyzon fossor, Ichthyomyzon greeleyi, Ichthyomyzon unicuspis, Petromyzon marinus, among which I. fossor and I. unicuspis are endangered, and other species are in concern. In 2011, 21 streams were inspected, 18 creeks were sampled by using an ammocoete backpack shocker designed in Dr. Stauffer's lab, and 4 species- Lampetra aepyptera, Lampetra appendix, Ichthyomyzon greeleyi and Petromyzon marinus were found in 14 creeks statewide. Lampreys were extinct at some sites because of flow regulation, channelization, poor water quality, and chemical treatments. In tributaries of Lake Erie, Sea Lamprey treatment might be a major reason to the population declining of other native species. Substrate size and water velocity are the most important factors determine the presence and absence of larval lampreys, so substrate samples were collected at 5 sites where ammocoetes were present. Differences on size of the sediments were found between lamprey spots and non-lamprey spots. Ammocoetes prefer smaller sized substrate with particle diameter less than 0.25mm in shallow, warm waters with dissolved organic matter. This study elaborated the current status of different larval lamprey species and indicated that their distributional range is shrinking and there might be a declining trend of native lamprey species although abundance survey was not implemented.