The ubiquitous soil fungi Fusarium oxysporum, Fusarium solani and Pseudallescheria boydii are frequently isolated from failed eggs in nests of flatback, green, hawksbill and loggerhead turtles at rookeries in eastern Australia. Within the nest, fungi first appears on an egg that has failed from natural causes. Using this nutrient source, hyphae then expand to adjacent, viable eggs and result in embryo mortality due to inhibition of the respiratory surface area or possibly to calcium deprivation. Since egg failure is the event that allows fungal colonisation of the egg mass, environmental factors resulting in embryo mortality are of paramount importance. Substrate conductivity appears to be the most important factor affecting hatch success. High substrate conductivity imposes osmotic stress on eggs and results in higher mortality and the increased availability of failed eggs to act as nutrient foci. Changing climatic conditions and long term rainfall patterns are therefore of great importance. Over time, an increasing occurrence of fungi on failed eggs seems to correspond with decreasing summer rainfall. Since rain leaches salts from the nest substrate, changing climate entailing reduced precipitation will result in an increasing substrate conductivity and higher embryo mortality from unfavourable nest conditions, allowing multiple foci for fungal invasion of the turtle nest and subsequent infection of viable eggs. This phenomenon has important consequences for the endangered loggerhead turtles nesting at the major rookery in eastern Australia-Mon Repos.