Monday 30 min Swim

Monday's swim was supposed to be Sunday, but due to the winter storm, all the county facilities were closed.  I adjusted my workout schedule this week to include a 30 min Monday swim.  These swims serve as a baseline for me, how am I doing? am I improving?  I must say that today's swim was tough, and overall, I did more of the workout this week than I did last week.  I did notice though, that the first half the workout is strong, good form, and my endurance is ok.  Towards the end though, no matter how hard I try, my form falls apart, and I need to take a break.  The promising news though, was the timed 100 yard sprint at the end - a 15 second improvement from the previous week, albeit small, it was still an improvement.