The hydrologic regime of the sea has a high degree of homogeneity. Annual fluctuations in mean monthly water temperatures at the surface does not exceed 3 ° C - 25 to 28 ° C. Over the past 50 years, the Caribbean has passed through three stages: cooling until 1974, a cold phase with peaks in 1974-1976 and 1984-1986. And then heating to 1986 at a speed of 0,6 ° C per year. Almost all the temperature extremes were associated with the phenomena of El Niño and La Niña. The salinity of sea water is about 36,0 ‰, the density 1,0235-1,0240 kg / m ³. On the surface of the water has a bluish-green and green. Vertical change in hydrological characteristics occurs to a depth of 1500 m below the sea filled with water from the Atlantic Ocean. Relatively shallow straits between the Antilles does not allow to penetrate into the Caribbean Sea deep ocean waters, whose temperature is less than 2 ° C. Deep currents are included in the Caribbean Sea through the Windward Passage and the Strait of Anegada, the water is rich in oxygen, has a temperature of from 4,2 to 4,3 ° C and slightly lower salinity (34,95-34,97 ‰). These waters are filled with Venezuelan Basin at depths of 1800-3000 m, and also penetrate into the Yucatan, Cayman, and Columbia Basin at a depth of about 2000 m. The sub-Antarctic waters of the middle layer includes the Caribbean Sea through the Strait of Anegada in the depths of 500-1000 m, and above them is subtropical underwater and surface currents.
Surface subtropical Caribbean during the passing of the south-east to north-western part of the sea, is a continuation of the Northern trade-wind flow, its flow is estimated at 26 million m ³ / with. Passat drives the water to the west coast of Central America during turns north and goes through the Yucatan Straits into the Gulf of Mexico. Current speed is 1-2,8 km / h, the Yucatan Channel increases to 6 km / h. During warm, the water temperature in it is about 28 ° C, and salinity - less than 35,5 ‰ because of the significant contribution of fresh water of the Amazon and Orinoco. Water pumped from the Caribbean Sea in the Gulf of Mexico, raises the level of the latter on the main part of the Atlantic Ocean (the water level at the western coast of Florida on 19 cm higher than the east), which creates a hydrostatic pressure, which is supposed to be the main driving force of the Gulf Stream .
In the southwestern area of the sea, between the coasts of Colombia and Nicaragua, for almost the entire year there is a circular flow, swirling counterclockwise. High tides in the waters of the Caribbean Sea mostly irregular semidiurnal, the amplitude of less than 1 m.
During the rainy season the water of the Orinoco create high concentrations of chlorophyll in the eastern part of the sea. Depression Karyako, located off the coast of Venezuela, is interesting because it is constantly present hydrogen sulfide, and the Cayman Trough revealed high concentrations of methane.