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. These substances leach into water and, in high traffic areas such as harbours and marinas, can affect animal life. There is a world wide trend towards limiting the use of TBT containing paints. Turtles, for example, often swallow floating plastic bags, mistaking them for jelly- fish.