Long before any settlers arrived, the original 1870 government survey of the area showed that just west of and parallel to the Atlantic Ocean's coastal dune was the "Boca Ratones Lagoon", which extended south for nine miles (14 km) measured from just north of the present location of Atlantic Avenue in Delray Beach.
Along the southern half of the lagoon were three wide areas each called a "Lake", which are now named (north to south) Lake Rogers, Lake Wyman, and Lake Boca Raton.
At the southeast end of the lagoon was a short protrusion toward the south which would become the Boca Raton Inlet after a sandbar at its mouth was removed.

The lagoon and lakes were part of a half-mile (0.8 km) wide swamp, west of which was scrub land a mile (1.6 km) wide (part of the Atlantic coastal ridge) where the Florida East Coast Railway (1896) and Dixie Highway (1923) were built.
To the west of the scrub was a half mile or wider swamp within which flowed north to south the "Prong of Hillsborough River", which is now the El Rio Canal.
It now forms the eastern border of Florida Atlantic University and the Old Floresta neighborhood.
The prong entered the "Hillsborough River" at the present eastern end of the straight portion of the Hillsboro Canal (dredged 1911–14), which is the southern city limits.
The river flowed southeast in several channels along the western edge of the present Deerfield Island County Park, formerly called Capone Island (named for Al Capone who owned it during the 1930s), which did not become an island until the Royal Palm Canal was dredged along its northern edge in 1961.
Flowing south from the lagoon to the river along the eastern edge of the 'island' was a "Small boat Pass into Hillsboro' River", also called the Little Hillsboro.
The river continued due south about four and a half miles (7.2 km) just inland of the coastal dune until it emptied into the Atlantic Ocean at the "Hillsborough Bar", now the Hillsboro Inlet.

The lagoon was dredged in 1894–95 to form part of the Florida East Coast Canal with a minimum depth of 5 feet (1.5 m) and a minimum width of 50 feet (15 m).
After 1895, the lagoon and canal were sometimes called the Spanish River.
Between 1930 and 1935 the canal was improved to 8 by 100 feet (2.4 by 30.5 metres) by the federal government and renamed the Intracoastal Waterway.
It was improved again between 1960 and 1965 to 10 by 125 feet (3.0 by 38.1 metres).
All three versions were subject to shoaling which reduced their depths below the specified minimum.
Forming part of the northern city limits is the C-15 canal, connecting the El Rio Canal to the Intracoastal Waterway.
Long before any settlers arrived, the original 1870 government survey of the area showed that just west of and parallel to the Atlantic Ocean's coastal dune was the "Boca Ratones Lagoon", which extended south for nine miles (14 km) measured from just north of the present location of Atlantic Avenue in Delray Beach. Along the southern half of the lagoon were three wide areas each called a "Lake", which are now named (north to south) Lake Rogers, Lake Wyman, and Lake Boca Raton. At the southeast end of the lagoon was a short protrusion toward the south which would become the Boca Raton Inlet after a sandbar at its mouth was removed.
The lagoon and lakes were part of a half-mile (0.8 km) wide swamp, west of which was scrub land a mile (1.6 km) wide (part of the Atlantic coastal ridge) where the Florida East Coast Railway (1896) and Dixie Highway (1923) were built. To the west of the scrub was a half mile or wider swamp within which flowed north to south the "Prong of Hillsborough River", which is now the El Rio Canal. It now forms the eastern border of Florida Atlantic University and the Old Floresta neighborhood. The prong entered the "Hillsborough River" at the present eastern end of the straight portion of the Hillsboro Canal (dredged 1911–14), which is the southern city limits. The river flowed southeast in several channels along the western edge of the present Deerfield Island County Park, formerly called Capone Island (named for Al Capone who owned it during the 1930s), which did not become an island until the Royal Palm Canal was dredged along its northern edge in 1961. Flowing south from the lagoon to the river along the eastern edge of the 'island' was a "Small boat Pass into Hillsboro' River", also called the Little Hillsboro. The river continued due south about four and a half miles (7.2 km) just inland of the coastal dune until it emptied into the Atlantic Ocean at the "Hillsborough Bar", now the Hillsboro Inlet.
The lagoon was dredged in 1894–95 to form part of the Florida East Coast Canal with a minimum depth of 5 feet (1.5 m) and a minimum width of 50 feet (15 m). After 1895, the lagoon and canal were sometimes called the Spanish River. Between 1930 and 1935 the canal was improved to 8 by 100 feet (2.4 by 30.5 metres) by the federal government and renamed the Intracoastal Waterway. It was improved again between 1960 and 1965 to 10 by 125 feet (3.0 by 38.1 metres). All three versions were subject to shoaling which reduced their depths below the specified minimum. Forming part of the northern city limits is the C-15 canal, connecting the El Rio Canal to the Intracoastal Waterway.
Boca Raton, Florida