The boundary with British Honduras was determined by a treaty of 1893 and is formed in great part by the Hondo river down to the head of Chetumal Bay, and thence through that bay to the Boca Bacalar Chicathe channel separating Yucatan from Ambergris Cay.
The Boca Grande outlet is the deepest, and is the main navigable entrance to the Orinoco at all seasons, the muddy bar usually maintaining a depth of 16 ft.
The Boca Grande was filled with stone after the city had been captured three times, because of the ease with which an enemy's ships could pass through it at any time, and the narrow and more easily defended Boca Chica, 7 m.
There were formerly two entrances to the harbour - the Boca Grande (large mouth) between the low sandy island or peninsula on which the city stands and the island of Tierra Bomba, and the Boca Chica (small mouth) at the south end of the latter island.
In his expedition (1531-1532) he entered its principal outlet, the Boca de Navios, and, at the cost of many lives, ascended to the junction of the Meta with the parent stream.