Sewage leaking into Lake Mille Lacs is threatening one of the state's most popular walleye fishing spots, pollution authorities say. Although both the tribe and its neighbors are concerned about the lake and its fishery, they also fear that failing septic systems will contaminate the ground water that they drink. "Everybody shares the aquifer," said Patricia Burke, environmental programs manager for the Mille Lacs band. "If anyone pollutes it, that affects all of us." Too much phosphorous, which comes from sewer leakage, could cause the clear, sandy-bottom lake to be overrun with algae, aquatic plants and silt, according to Bob Newport, a water quality specialist with the Environmental Protection Agency in Chicago. That transformation would change Mille Lacs from a haven for walleye into a system dominated by sunfish and bass. State, federal and tribal officials plan to meet with area residents to discuss a proposed $23 million sewage treatment plant that would be built and operated by the band. Untreated sewage is a problem because the communities along the western shore use individual septic systems, which have largely failed. A recent study for the city of Garrison concluded that more than 95 percent of its septic systems are "imminent health threats, failing or nonexistent.