These methods include dynamite blasting and cyanide fishing. Overfishing not only depletes fish stocks of target species, but also changes the dynamics of the entire reef. Decreases in herbivores can lead to algal blooms which overtop coral growth and can cause mass mortality. Over 100,000 oil tankers and container and cargo vessels transit the Straits of Malacca and Singapore each year. Spills occur mostly by collisions or grounding.
Ships deliberately dump oil wastes into the water.
It is likely that they do this after cleaning the tanks to avoid having to pay to have them cleaned. Some areas can have more than 25 oil slicks in a 10,000 sq. Oil slicks can be 100 km long and 3 km wide, double the length of Singapore. The smaller ones are still 100m by 100m. In January 1993, another tanker crashed into a ship off the northern coast of Sumatra and spilled 15,000 tons of oil into the Malacca Straits.