Algae Bloom in Florida (Photo for Example) – By John Moran [Public domain], via Wikimedia Commons
Farmers do their best, but they can’t control what happens to excess fertilizer. And this is the result.
Runoff is an important element about the sustainability of agriculture. Its not sustainable method of growing if you are destroying or hurting the environment beyond your farm.
Indoor farms use exactly what is needed and there is no runoff.