I've been lake swimming several times over the last couple of months. Seems the tri clubs etc are bound by their insurance or the venues insurance as to what is an acceptable temperature.
I got to thinking about a few years ago, when I did kayaking, I'd be in rivers and the North Sea 12 months of the year.
I did a bit of searching through Facebook, starting with the Outdoor Swimming Society. Follow a few peoples profiles and you can eventually find groups or events (It's kind of like the 6 degrees of separation thing?)
I eventually found a group called the 'Dove Dippers'. Luckily one of their venues is on my doorstep. It's not an official 'club' just a group of people into swimming outdoors. No joining fees, no session fees. Just turn up and swim at your own risk, but not on your own.
Theres a wide range, from newbies to those training for channel swims. Some don't bother with wetsuits, they're acclimatised for year round swimming.
Another difference for me is, the tri clubs tend to have very structured training sessions? These is more 'up to you'. You can get in and swim 800m, ideally in a straight line.
My 'local' temp was 13C on wednesday, prior to that its been 10/11 for the last month or two.
Nice to swim regularly and get used to how your wetsuit actually fits etc.