Bioluminescent bacteria are most abundant in marine environments during spring blooms when there are high nutrient concentrations. These light-emitting organisms are found mainly in coastal waters near the outflow of rivers, such as the northern Adriatic Sea, Gulf of Trieste, northwestern part of the Caspian Sea, coast of Africa and many more. These are known as milky seas. Bioluminescent bacteria are also found in freshwater and terrestrial environments but are less wide spread than in seawater environments. They are found globally, as free-living, symbiotic or parasitic forms  and possibly as opportunistic pathogens. Factors that affect the distribution of bioluminescent bacteria include temperature, salinity, nutrient concentration, pH level and solar radiation. For example, Aliivibrio fischeri grows favourably in environments that have temperatures between 5 and 30 °C and a pH that is less than 6.8; whereas, Photobacterium phosphoreum thrives in conditions that have temperatures between 5 and 25 °C and a pH that is less than 7.0.