Pilgrim Lake is also known as East Harbor.

In 1868 the mouth of the East Harbor was diked, to facilitate the laying of track for the arrival of the railroad; the wooden bridge and sand road were finally replaced by a formal roadway in 1877, as shown in the accompanying map from 1887. The East Harbor thus became a lake, connected to Provincetown Harbor only through a culvert in the dike, and in 1910, the U.S. Geologic Survey (USGS) officially renamed it Pilgrim Lake.