It's very strange.  I fished the Rideau River between the Bronson Bridge and Hogg's Back intensively in the early 1970s, and just returned for a few visits in the last couple of years - incredible changes.  The water is now very clear whereas it used to be murky green and aquatic vegetation is much more abundant, with zebra mussel debris everywhere.

Yellow Perch, Rock Bass and Northern Pike seem to have disappeared.  Walleye have either disappeared or are inactive during the day due to the clear water (that has resulted from Zebra Mussels), either way I have not seen or hooked any in the areas where they used to be easy to get.  The Muskellunge fishing is now fantastic though, and Smallmouth Bass are still present although not as abundant as in the old days.