I had another wonderful swim at Parliament Hill lido today, swimming a continuous 6k . The water was 18 degrees . Cold, but not cold enough.
I drank some Endura before and during my swim along with a couple of Clif Blocks energy chews.
I started out at quite a fast pace but at about 5k I found my concentration was starting to go and though I maintained a decent pace I was running low on energy.
Maybe I was dehydrated. I only took a one sip of Endura during my swim, but I think I should have taken one every 30 minutes, or every 2k.
I might go back tomorrow and try again.