BAILEYVILLE — Alewives are expected to swim upriver of the Grand Falls dam on eastern Maine’s St. Croix River this week for the first time in 22 years.

Lawmakers passed a law this spring allowing the fish, also known as river herring, to swim upriver of the dam, overriding an earlier law that closed a fish passage at the Grand Falls dam to alewives. The earlier law was passed at the request of fishing guides who maintained the fish posed a threat to smallmouth bass populations in waters upriver of the dam.

As of Monday, more than 600 alewives had swum past the Woodland dam, about 10 miles downriver from the Grand Falls dam. With the fish passage open once again, the St. Croix — which is the border between Maine and New Brunswick — in time could have the largest alewife run in the country, according to supporters of the new law.

“Our ancestors would be very proud today. The arrival of alewives at the Grand Falls flowage of the St. Croix River is a historic event for the Passamaquoddy people, and for all of our neighbors in Maine and Canada,” said Brian Altvater, head of the Passamaquoddy tribal group, Schoodic Riverkeepers.

Opening the St. Croix River watershed to alewives will benefit the Passamaquoddies, Maine’s commercial fishing industry, and fish and wildlife throughout the Gulf of Maine, he said.