Why is Lake Ontario the most polluted?

Answer 1

The problem with Lake Ontario is mostly its elevation. AS the lowest lying Great Lake, it accumulates the down stream runoff from all the other lakes. Also add to the fact it's location as an old industial waterway (steel mills of Ohio) and its history of pollution has been decades. It's slowly recovering now because those mills are mostly in the southern USA. Today's problem is mostly with Nuclear Power Plants and their warm water. Nuclear Plants usually need a huge volume of cold water to cool their super hot reactors. In the Midwest, most plants are required to hold this superheated water for a few weeks and then release it when cool. That does not happen on the Lake as power companies release warm water, effluent release temperature is dictates as part of plant licensing, following an environmental impact study. The lake also suffers from foreign population as large ocean going ships dump water, usually polluted water from Asian shores (used to balance the ship when empty), into the waterways. Hence how the zebra mussel got there. It's just location, of being the lowest in elevation, heart of the old American industrial heartland, and doorway to the rest of the inner Great Lakes, makes the Lake a hallway that people wipe their feet at when entering the countries interior.