Prevailing winds, ocean currents, and deep water trenches can often combine to produce conditions that are optimum for fishing. In areas such as the Pacific coast of Central and South America, offshore winds push the warm surface waters out to deeper waters. Underwater currents push cold, nutrient-rich water from deep below the surface back toward the coast. The high concentration of nutrients in this colder water, caused by decomposition of organic matter at extreme depths, creates an ideal environment for fish and other sea life. Civilizations with access to areas such as this can significantly increase their food supply by establishing a thriving fishing industry.