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
Open and closed lakes open lakes are usually fresh water: dissolved solids do not accumulate. Open lakes form in areas where precipitation is greater than evaporation. Because most of the world's water is found in areas of highly effective rainfall, most lakes are open lakes whose water eventually reaches the sea. For instance, the Great Lakes' water flows into the St. Lawrence River and eventually the Atlantic Ocean. Open lakes typically have stable levels which do not fluctuate because input is always matched by outflow to rivers downstream. If more water enters an open lake than was previously leaving it, then more water will