Fertilizers are generally considered an effective tool in the fight for better lawns, vegetables, flowers and fruits. One of the unintended effects of fertilizer is the toll it takes on lakes, ponds and the wildlife they contain. Knowing the effects may cause you to think twice about applying fertilizer near open water.
Manure and fertilizer, when placed onto a lawn or in a garden, may wash off or drain into a nearby lake, causing oxygen depletion. When nutrients are released from the fertilizer, microorganisms feed on it and grow at a fast rate. As the microorganisms reproduce, their bodies dissolve the oxygen content of the water they're living in. This causes other plants and animals to die away over time.
Fertilizers may also cause the excited growth of both aquatic plants and weeds. One pound of phosphorous added to lake or pond water can produce more than 100 lbs. of new aquatic plant life, which will compete with other plants and animals for oxygen. Also, algae may grow in the water with the addition of fertilizer. Blue-green algae can be toxic to humans, causing skin rashes, stomach and respiratory problems. It can also kill livestock that comes in contact with it.
Fresh manure fertilizer contain ammonia, which can wash off into water supplies. Ammonia is toxic to wildlife, destroying their ability to absorb oxygen from the water. If enough plants die, this will kill the ecosystem for any fish living in the water, starving them to death. High enough volumes of ammonia will kill fish without starvation.