Eutrophication is the process by which water bodies become enriched with nutrients—primarily nitrogen and phosphorus—leading to excessive plant and algae growth. While some nutrient input is natural, human activities dramatically accelerate eutrophication through agricultural fertilizer runoff, sewage discharge, stormwater carrying lawn fertilizers, and industrial effluents. Excessive algae growth creates "blooms" that block sunlight from reaching underwater plants, and when algae die and decompose, the process depletes oxygen, creating "dead zones" where fish and other aquatic life cannot survive. Blue-green algae (cyanobacteria) blooms can produce toxins dangerous to humans, pets, and wildlife. Municipalities address eutrophication through wastewater treatment upgrades to remove nutrients, stormwater management, restrictions on lawn fertilizers near water, and protection of vegetated buffers along shorelines. Lake Erie and Lake Winnipeg have experienced significant eutrophication problems.