A problem that arises when the nutrient level in an aquatic ecosystem exceeds the critical load is
Eutrophication is the aging of a lake by nutrient enrichment of its water. During the past century, lakes in many parts of the earth have been severely eutrophied by sewage and agricultural and industrial wastes. The prime contaminants are nitrates and phosphates, which act as plant nutrients. Critical load is the amount of added nutrients that do not damage the integrity of the ecosystem.