Abstract: Nile tilapia, Oreochromis niloticus is one of the most common and available fish for Egyptians. Fish health can be conflicted with 2 main factors; fish diseases and environmental pollution both of them are complementary to each other. Fish diseases are arising from either infectious or non-infectious causes. Infectious diseases as viral, bacterial, mycotic and parasitic diseases usually accompanied with high mortality and morbidity rates. Recently, few viruses as Tilapia Lake Virus have been incriminated in fish mass mortalities across the Egyptian aquaculture. Bacteria are critically dangerous pathogens for both cultured and wild fish responsible for mass losses in fish production. Mycotic diseases are among the main diseases causing severe economic losses to Nile tilapia especially Saprolegniasis. Mycotoxins are the most toxic and common contaminants that also degenerate vitamins in fish feed. Finally, parasites are the cornerstone of all fish outbreaks that associated with secondary infection with virus, bacteria and/or fungi. Non-infectious diseases mainly caused by environmental problems and nutritional deficiencies. Water pollution is a worldwide problem that has a large concern due to industrial and agriculture progress and many anthropogenic activities. The application of hygienic and preventive measures of the environment competently tightens the biosecurity of fish facility. Vaccination and the use of probiotics and medicinal plants as an alternative to chemotherapeutic treatment have become an important aspect of aquaculture. The present review presents Nile tilapia diseases, their causes, prevalence and control. Also it provides the different types of water pollution and its relation to fish diseases.