Biologists are trying to figure out why American eels are washing up dead on the shores of northern Lake Champlain.
Vermont Public Radio reports at least 15 dead eels have appeared from Swanton south to Milton in the past few weeks.
State Fish and Wildlife Department fisheries biologist Bernie Pientka said it's not clear what's causing the die-off. He said an invasive nematode, or roundworm, has harmed eel populations in the U.S. Southeast, so that may be a cause.
Pientka said other fish species in the lake do not seem to be affected.
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Lake Champlain once supported a commercial eel fishery. The population declined in the 1980s and 1990s, but rebounded after eel ladders were upgraded on the Richelieu River, which flows north from Champlain to the St. Lawrence River.