The lake your talking about is called Bannister Lake, I was born and raised in Cambridge and used to fish it ALL the time.. When I was younger it produce decent size Pike and tons of them, same went for Crappies and Smallies, but 10+ years back they redid the coulvert (spelling?) And that basically killed off all the fish for years. I hadn't fished it since then until this year and caught some small Pike and Crappies, the fishing is slowly coming back but I can't see it booming for another 5+ years.
As for the bridge in Ayr, I have never fished it myself but I do fish a couple bridges close to Drumbo on the Nith and they've produced decent size Smallies, Pike, Carp and Suckers.