The Mackay River is a 13.4 miles (21.6 km) tidal river in Glynn County, Georgia

Glynn County, Georgia

Glynn County is a county located in the U.S. state of Georgia. As of 2000, the population was 67,568. The 2008 Census Estimate showed a population of 75,884...

. It flows between Saint Simons Island to the east and the mainland, including the city of Brunswick

Brunswick, Georgia

Brunswick is the major urban and economic center in southeastern Georgia in the United States. The municipality is located on a harbor near the Atlantic Ocean, approximately 30 miles north of Florida and 70 miles south of South Carolina. Brunswick is bordered on the east by the Atlantic...

, to the west, and connects to Buttermilk Sound at its north end and St. Simons Sound

St. Simons Sound

St. Simons Sound is a sound in Georgia that lies between Jekyll Island and St. Simons Island. It is part of the waterway from the Atlantic Ocean to the South Brunswick River to the port at Brunswick, Georgia. The St. Simons lighthouse stands on the north side of the sound....

 and the Brunswick River

Brunswick River (Georgia)

The Brunswick River is a tidal river in Georgia. It begins at the Sidney Lanier Bridge at Brunswick, Georgia, at the confluence of the Turtle River with the East River, and flows east to St. Simons Sound, the strait between Saint Simons Island to the north and Jekyll Island to the south.-...

 at its south end. It runs parallel to and west of the Frederica River

Frederica River

The Frederica River is an tidal river in Glynn County, Georgia. It forms the western boundary of Saint Simons Island of the Georgia Sea Islands. Fort Frederica National Monument is located on the eastern bank of the river on Saint Simons Island....

. The Mackay River is crossed by Route 63 traveling between Brunswick and Saint Simons.