The Great Lakes are really freshwater seas. They contain about 18% of the fresh surface water in the U.S. and can be treacherous for boaters and swimmers who underestimate their power.
Right now fish are migrating toward their spawning places in the lakes and in tributary streams. Pacific salmon that were planted in the Great Lakes will die after they spawn. Lake trout, a native species will continue to live after they spawn.
For more information about the Great Lakes and their biota, read my book, The Dynamic Great Lakes, available at bn.com, Amazon, and many independent bookstores.