Check all statements that are true. question 2 options: too much nitrogen and phosphorous in the water cause algae to bloom. the nitrogen and phosphorous usually get into the water supply from point sources. algae blocks sunlight from reaching the native water plants, removing the food supply for fish. when large algal blooms die off, the oxygen levels in the water drop and fish suffocate. large algal blooms can be harmful to people and to the commercial fishing industry.