The excessive growth of algae and aquatic plants caused by nutrient overload creates a greenish color to the water. As nutrient loads increase, the green becomes more intense and plant life becomes more lush. Intense algal blooms, thick mats of algae, or dense stands of aquatic plants degrade water quality and habitat. When dairy cattle or other livestock are allowed to enter streams, they often defecate in them, contaminating the stream with harmful pathogens and nutrients. Manure from livestock may also enter the water from runoff of grazing land adjacent to the stream.
Manure increases the loading of nutrients and decreases dissolved oxygen demand.
Animal droppings in or around streams, on the streambank, or in the adjacent riparian zone, or well-worn livestock paths near streams suggest the probability of manure in the stream. Areas with stagnant or slow-moving water may have moderate to dense amounts of vegetation or algal blooms, indicating localized enrichment from manure. Many farmers recognize that fencing animals out of streams is the right thing to do environmentally, but continue to allow access because the stream is the animal s source of water. Recent research suggests that providing alternative water sources to livestock may be desirable for animal health as well as for water quality. Cattle preferred an alternative source over the stream, even during hot weather when they had to walk a good distance.