Horse wastes can also contaminate aquatic habitats directly. In large concentrations, both nitrogen and phosphorus can be toxic. Salt from horse waste can kill fish and other aquatic life. And fish are particularly sensitive to ammonia, a byproduct of bacterial conversion of urea, a principal constituent of urine and other animal waste. Fortunately, responsible animal management can minimize all of these threats - so that we can keep our horses and keep our aquatic ecosystems healthy.
All aquatic life depends on the small amount of dissolved oxygen that naturally exists in water.
The addition of any decomposable organic material to water stimulates the growth of aerobic bacteria that break down, or consume the organic matter. The respiratory demand of the resultant bacterial population can become large enough to overwhelm the water's oxygen dynamics, leaving little or no dissolved oxygen for other aquatic life. Many of the nutrients ingested by animals, not just horses, return to the environment in feces and urine. On land, moisture and atmospheric oxygen support the bacterial conversion of theses wastes to nutrients available for plants. However, when carried by stormwater runoff to streams and lakes, excessive amount of these same nutrients can stimulate unwanted algae blooms.