shelter the estuaries of the Essex and Annisquam rivers. Not included are the grasslands south of Cape Ann nor the grasslands north of the mouth of the Merrimack River. The entire coast of Massachusetts comprises this type of estuarial terrain, except for the rocky outcrops. Great Marsh has been the focus of a coalition of environmental groups and agencies to protect the marshes between Cape Ann and the Merrimack River from degradation. Historically this coalition continues the work of the founding fathers of Ipswich and other towns in the area, who found it necessary to protect the marsh from overgrazing by means of legislation. Beach Plum Island Beach is a gently sloping shelf extending some distance out to sea. As a result of the slope, tidal flow does not reach very far horizontally, while breakers are small and close to shore. Boats can easily be launched from or landed on the beach. The shelf causes strong undertow currents. During severe storms the beach is inundated and the breakers strike the dune line. A number of ships have been wrecked in the shallow waters off Plum Island Beach. The Labrador Current flows from north to south along the shore, migrating sand in that direction and chilling the coastal waters. Several breakwaters have been constructed along the north coast of the island to protect the beach and impede the process. The migrating sand moves the outlet of the Merrimack River, which has been artificially fixed at its current location. Vascular plants On the dunes a fragile cover of beach grass, beach pea and beach heather stabilize the sand. Visitors to the refuge are restricted from the dunes except on boardwalks to protect this cover. Destabilization has been a problem. In 1953 the U.S. Soil Conservation Service planted several thousand black pines, a hardy alpine tree, to help hold the sand. Stands of black pine, pitch pine and occasional eastern red cedar trees can be found in the depressions between the dunes. There also are thickets of beach plum, from which the island takes its name, as well as bayberry and honeysuckle (the latter being intrusive). Maximum dune elevation is about . In the deeper depressions and more sheltered regions between or next to the higher dunes are vernal pools in which black oak, red maple and black cherry can be found. In the underbrush are cranberry. The ferns, moss and leaf cover