Gee, this is the first I'd heard of it. According to the Detroit Free Press, the storage began in the 1960s or late 1950s, on the US and Canada sides of all the Great Lakes. According to the article (October 2018), "Spent nuclear fuel sits not far from the shores of four Great lakes - Michigan, Huron, Erie, and Ontario - at 15 currently operating or former nuclear power plant sites, including four sites in Michigan."
I was born in Detroit and drank Great Lakes water 1948-70. My sister died of ALS two years ago, but the rest of us haven't had health problems that I'd relate to nuclear waste.
Nonetheless, it's scary.
I gather that most of the waste was from nuclear power plants, more on the Canadian side than on U.S. shores. All of those Rust Belt cities were drinking water from the Great Lakes.
-Joe-