A settlement with federal authorities will require the city of Unalaska to spend at least $18 million on its sewage treatment plant.
The U.S. Department of Justice says in an announcement the settlement was for action taken on behalf of the Environmental Protection Agency.
A lawsuit last year contended that the city continually violated its pollution permit with discharges in South Unalaska Bay.
The Justice Department says monitoring reports indicated Unalaska's treatment plant had more than 5,500 violations of permit limits between October 2004 and September 2011. Some were discharges of fecal coliform bacteria more than double what was permitted.
Unalaska and Dutch Harbor are about 800 miles southwest of Anchorage in the Aleutian Islands. The port is the home base for large-scale commercial fishing in the Bering Sea.