Complex sentence: In increase in nutrients, from fertilizer, for example often create conditions conducive to algae blooms, which has poluted the water with a toxic blue substance and a foul smell, making the water unusable.
Split into simpler sentences: In increase in nutrients, from fertilizer, for example often create conditions conducive to algae blooms. The algae has given the water a blue color and a foul smell, making the water unusable.