Matanzas Bay spreads in front of you here in St. Johns County, Florida, where the South Atlantic pushes in through the St. Augustine inlet. Technically this stretch of water running along the city's waterfront is part of the Matanzas River, though locals often call it a bay or harbor. Clockwise from the inlet the waters connect to Salt Run — an inlet of Anastasia Island that creates a peninsula of the eastern portion of Anastasia State Park — and to the Matanzas River itself, a tidal channel and part of the Intracoastal Waterway that flows easterly then south for approximately 15 miles, separating Anastasia Island from the mainland.
The San Sebastian River flows westerly from the Matanzas River and creates a peninsula of the original Spanish-era section of St. Augustine. Nearby Hospital Creek is a tidal channel flowing north from the confluence of Matanzas Bay and the North River; this is the creek into which Pedro Menéndez de Avilés sailed and initially established St. Augustine on its mainland shore. The Tolomato River — also known locally and historically in the British period as the North River — flows north.
Salt Run, the Matanzas River, the San Sebastian and the Tolomato all feed this one tidal system that meets the sea at the inlet.