Great Lakes Areas of Concern rivers, and oceans causing pollution and buildup of sediment. Nonpoint source pollution is said to be the most problematic and hardest to reverse of the types of pollution because it is so hard to regulate and pinpoint where it originates. Many experts agree that nonpoint source pollution is the biggest concern facing the Great Lakes. With the increase of urbanization, a toll has been taken on the lakes in these areas. Lakes that once had stable ecosystems with the appropriate amount of plant life are now full of massive amounts of plants and algae that have been fed by excess
Great Lakes during the 1970s and 1980s, combined with successful salmonid stocking programs, have enabled the growth of a large recreational fishery. The last commercial fisherman left Milwaukee in 2011 because of overfishing and anthropogenic changes to the biosphere. Since the 19th century an estimated 160 new species have found their way into the Great Lakes ecosystem; many have become invasive; the overseas ship ballast and ship hull parasitism are causing severe economic and ecological impacts. According to the Inland Seas Education Association, on average a new species enters the Great Lakes every eight months. Introductions into the Great Lakes include the