Since its first discovery in Lake Ontario in August 1998, Cercopagis pengoi spread inland to six of New York’s Finger Lakes (Seneca, Cayuga, Otisco, Canandaigua, Owasco and Keuka) within a year, possibly on fishery sampling gear, in bait buckets, or on recreational angling equipment. In these inland lakes, Cercopagis now dominates the offshore zooplankton community during the summer and fall. This species has also been found in Grand Traverse Bay and southern Lake Michigan and in western Lake Erie and the Detroit River. It is expected to spread throughout the Great Lakes by means of currents, inter- and intra-lake ballast transfers and recreational boating and angling. The fishhook water flea, like the spiny water flea, fouls fishing lines, down rigger cables and fish nets, in many cases to an extent that anglers have had to cut their lines and lose fish because of reel clogging. The species’ length, including body and spine, can exceed 1 cm.
It is unknown what the future impacts of Cercopagis are going to be. It is possible that the high population densities of the species will create significant predation pressure on smaller cladocerans to impact the size and composition of native phytoplankton communities. Furthermore, Cercopagis may compete with native young- of-the-year fish populations for small prey. It is also possible that the species may become prey itself for larger fish. It is not known, therefore, whether Cercopagis will ultimately be an energetic source or sink in the Great Lakes.