Nonpoint source pollution can severely affect many aspects of a community especially the commercial fishing industry. Nonpoint source pollution can lead to massive fishkills due to severely decreased levels of oxygen in the water, a condition known as hypoxia. In addition, fish and shellfish can be poisoned by harmful algal blooms caused by an overabundance of nutrients in the water, a condition called eutrophication. Photo: Duluth, Minnesota. Minnesota Sea Grant.