Over the last 100 years, agricultural expansion and intensification has led to changes in water quality and the health of stream ecosystems. Considerable increases in fertilizer and pesticide use began in the 1960s. In 2010, about 11 billion kilograms of nitrogen fertilizer and 300 million kilograms of pesticides were used annually to enhance crop production or control pests. Increased levels of nutrients from fertilizers draining into streams can stimulate algal blooms and affect stream health and recreational uses of local streams, downstream reservoirs, and estuaries, and increase treatment costs for drinking water. Pesticides that are transported to streams can pose risks for aquatic life and fish-eating wildlife and drinking-water supplies.