Algal bloom causes by eutrophication (when excess nutrients run into a body of water). Eutrophication provides nutrients for algal bloom. As a result, there is an increasing in algal bloom population. Increasing in algal bloom population can block the light that is needed by other organisms. This could impact these organisms survival. Furthermore, when these algae die, their body sink into the bottom of the sea, which consider as nutrients for bacteria, increasing bacteria population. This means that the respiration rate by bacteria is increasing as well. When bacteria respire, they need to absorb oxygen. Over time, these oxygen level will eventually decrease and later form a dead zone.
