The population of algae in the water increases due to the excess amount of nutrients such as nitrogen and phosphorous, which are provided from the run off from the farmlands. Due to this higher nutrients, the amount of dissolve oxygen decreases drastically, and aquatic plants cannot undergo the process of photosynthesis. This directly affects the organisms that lives in the fresh water and marine ecosystem, as it will be difficult for them to survive.
Thus, the excess amount of algae in water makes it unsuitable for drinking, agricultural purpose and also leads to the reduction of aquatic species.
well AU is only for inside a star system and the number of AU would be too high, so light years are easier its like saying ur 6 feet instead of 72 inches or in centimeters
