Piscataqua River Watershed
New Castle sits in the mouth of the Piscataqua River. The water here is a mix of fresh water from the river and salt water from the Gulf of Maine. Being a small island, New Castle has no significant freshwater resources. Several small ponds and marshes are scattered throughout the town. The land is densely developed with homes and businesses, including a large resort on Wentworth Road. The shoreline of New Castle includes numerous beaches and rock ledges, many of which have been fortified by seawalls.