Holiday so far

I'm on summer break from work at the moment. Haven't done much apart from read, knit and some housework.
Today though , I decided it was time I tried to get back swimming.  As I haven't been for such a long time.  I went at noon and managed to swim 16 lengths, which is quarter of a mile.  I didn't push myself for more, as I felt I needed to get used to swimming again.  The other reason being, I had walked there, so had to factor in the walk back home, so swimming until I was exhausted would have been a very bad move. 
I feel good , but now one of my knees feels like it wants to bend wrong way when I walk.
I hope I can keep it up.  There is really no good reason why I shouldn't swim more, apart from fitting it in, and the holiday seemed to be the best time to get into a routine about it.