Unlike many countries in Europe and the USA, South Africa does not dump industrial wastes or sewage sludges. Decomposition of organic matter causes a drop in dissolved oxygen, particularly in calm weather and sheltered bays. These blooms can discolour the water, clog fish gills, or even be toxic, e.g. red tides. Microbial breakdown of dead algae can cause oxygen deficiencies. Water quality guidelines specify maximum levels of pollutants allowed in the receiving water.
Oil spills smother plants and animals, preventing respiration.
In seabirds and mammals it can cause a breakdown in their thermal insulation. Chemical toxicity can cause behavioral changes, physiological damage, or impair reproduction. Oil pollution is an eyesore, and cleanup and subsequent disposal of oily wastes is difficult. Pesticides, such as DDT, and other persistent chemicals e.g. PCBs, accumulate in the fatty tissue of animals. These chemicals can cause reproductive failure in marine mammals and birds.