Archeological evidence suggests that Watertown was inhabited for thousands of years before the arrival of settlers from England. Two tribes of Massachusett, the Pequossette and the Nonantum, had settlements on the banks of the river later called the Charles. The Pequossette built a fishing weir to trap herring at the site of the current Watertown Dam. The annual fish migration, as both alewife and blueback herring swim upstream from their adult home in the sea to spawn in the fresh water where they were hatched, still occurs every spring.