Answer: Encouraging algae growth
Step-by-step explanation:
Algae are tiny single celled aquatic plants which are found in colonies over the surface of water body and on the shorelines of the water body. The algal growth restricts the natural flow and circulation in the water body. If the water body consists of high concentration of phosphates and nitrogen this will lead to abundance in the algal growth. The algal bloom is likely to deteriorate the quality of freshwater as it will lead to the depletion of oxygen in the water body. This will likely to affect the aquatic food chain in the water body.
Hence, encouraging algae growth is not one of the three keys to keep water clean.
The following are the three keys which can be used to keep water clean.
Reduction of pollutants.
Effective cleanup of oil and gasoline spills.
Proper sewage treatment.