Corals can not survive in freshwater or near a freshwater input as they are completely intolerant to changes in salinities, which is the main reason as to why there can be no corals found near river deltas. The most significant example of this is that no corals can be found at the mouth of the Amazon River going into the sea. Another way in which corals can be affected is if a rapid input of freshwater from events such as storms which have been proven to start coral bleaching events. These events are relatively rare, small and close to shore. The reduced salinity is also a cause for localised bleaching events.