This massive river in South America floods out of Venezuela and is picked up by the Guyana current and carried north to Trinidad and Tobago. This rush of fresh water affects the water temperature, salinity, and turbidity. Green or a flowing yellow stream creating unusual light underwater replaces the clear turquoise of the winter months. The turbidity is caused by algae particles suspended in the water and attracts large numbers of fish. Fifty-eighty foot viz in the winter can drop to 30 feet in the summer with poor viz sometimes only at the top 15 feet or so.
Many dives are around rocks that have become encrusted with sponges and coral.
Huge barrel and vase sponges, rope sponges, bright encrusting and boring sponges make color and texture variety on the reef. Since sponges attract Angelfish, you will see many and large specimens of these species in Tobago. Mantas do frequent the Speyside area of Tobago, but don't count on seeing them, sometimes they don't put in an appearance. Tobago diving has a great deal of variety including a wreck dive. The top of the wreck is at 50 feet.