The cold!

Just as i was starting to feel a little more confident, i went for a swim in Lake Passy nr Chamonix which was 16-17 degrees (not far off the Channel temp in August). I felt cold during most of the swim and started shivering at about 1hr 20 and eventually got out at 1hr 40mins. Went back again today and managed 2hrs and felt less cold/no shivering. The acclimitisation is a real worry although i am trying to add a few layers of fat on to counter this (thanks to the guys for helping out during 3 man over the last 2 weekends!). I think from now on, swimming in the cold is a must to try and get used to it, although the expletives dont seem to stop when i first enter the water no matter how many times i go in. Nothing on Google to help apart from get in the cold water more or wear a wetsuit (thanks - not allowed). This will be my biggest week of training so far as i should do more than 41km of swimming, mostly in cold water. I had a dog jump in the water after me today which i thought was quite sweet as most dogs turn round after about 5m but this one was still chasing me after about 30m and closing which made me put my head down for a sprint. NOt sure what would happen if you met an inquisitive dog 30 m out in a lake but didnt really want to find out...!
Thanks to those who have already helped me out - Obviously George and Bertie, Dave Joyce the sports science guru, Frodo and Laura for swimming with me, Martin Shyvers for helping on a weights programme, Julie Bradshaw for her input and Charles Noble for general info and help.