How can leaching cause bad smells in lakes?

Leaching is the process by which nitrates and other organic molecules can reach lakes from fields. This may be due to a large amount of fertiliser being applied or heavy rain causing the fertiliser to wash into lakes.Nitrates are essential for organism growth as they can be assimilated (taken in) and used for protein synthesis. In this case, the nitrates can be used by algae to grow and rapidly reproduce. This creates large clumps of algae called Algal Blooms. The algal blooms will cover the surface of the water thus allowing no/limited sunlight to reach the plants on the bed of the lake.This means they cant photosynthesise and die, this lowers the oxygen concentration in the lake as no more oxygen is produced by these plants (as a bi-prouct of photosynthesis). Aerobically respiring bacteria break down the dead plant matter thus further decreasing the oxygen concentration. This creates a toxic enviroment for fish and other larger species due to the high levels of Carbon Dioxide. They will also die. Anaerobically respiring bacteria will break down the dead fish and release toxic and smelly gasses such as sulfur dioxide