Less fish, more duck

I went for a swim today for the first time in a long time.  I have got out of the habit somewhat and it was telling.  Just about managed 55 mins, no idea how far I swam as I am terrible at keeping track.  It was pretty tiring.  I aim to start going a bit more again as I want to do some open water swimming this summer and perhaps enter an aquathlon (swim, run).  Need to work on my stamina and probably my technique. Perhaps lessons?