Niagara Falls will split during the widening of the St. Lawrence Seaway, as will all natural and manmade barriers between the Great Lakes and the Atlantic. This will change the level of the lakes, and the drainage patterns, to some degree, depending upon the level of bordering land and the ocean tides. Salt water will be detected all the way up to Lake Michigan and Lake Superior, which will appear to be the fresh water lakes they are now. Niagara Falls appears dramatic only because the water way spills suddenly, rather than gradually, and being shattered and spread during the widening of the seaway, the falls will become merely rock walls along the new course of the waterway. Thus, the great seaway will become a mode of travel, and cities along this course such as Buffalo and Hamilton can anticipate being travel stops and point of commerce among survivors.
Note New Madrid Sequence commentary.
Note New Madrid commentary.