eutrophication
The nitrogen and phosphorus rich compounds found in sewage act as fertilisers and encourage rapid growth of marine plants. In many cases the environmental damage is minimal, but in sheltered bays or semi-enclosed bodies of water such as lagoons or estuaries, the constant "fertilisation" of the environment from discharges of sewage can lead to serious harm to marine ecosystems. In areas with coral reefs, even small amounts of nutrients discharged at regular intervals can lead to a dramatic loss of live coral, which becomes smothered by a proliferation of marine algae (see photo). The damage is most noticeable in popular boat anchorages, which were once the beautiful and pristine locations to visit.
More generally eutrophication leads to a decrease in biodiversity, with only as a small number of marine plants dominating the seabed. In some cases, it can also lead to a reduction in oxygen levels at night, making the environment unfavourable for many species of fish and other animals.
References:
Silbiger NJ, Nelson CE, Remple K, Sevilla JK, Quinlan ZA, Putnam HM, Fox MD, Donahue MJ. 2018 Nutrient pollution disrupts key ecosystem functions on coral reefs. Proc. R. Soc. B 285: 20172718. http://dx.doi.org/10.1098/rspb.2017.2718
Chislock, M. F., Doster, E., Zitomer, R. A. & Wilson, A. E. (2013) Eutrophication: Causes, Consequences, and Controls in Aquatic Ecosystems. Nature Education Knowledge 4(4):10Eutrophication threatens Caribbean seagrasses – An example from Curaçao and Bonaire
https://www.sciencedirect.com/science/article/abs/pii/S0025326X14005955?via%3Dihub
Clean Water for Reefs
https://coral.org/what-we-do/clean-water-for-reefs/
Eutrophication in coastal waters
