Swim - getting slower?

Found time for a 40-minute swim today. 400m warm up, and then a few sets of 2 lengths arms-only, concentrating on what the hell I do with my arms after they are in the water, plus 2 lengths "fists", trying to find the action with the best pull. Maybe 24-28 lengths all in. Finished off with a 400m continuous swim, trying in vain to find the 8:46 form from Waveney last year - I was 9:50. And I thought I had done quite well. Still, not a bad little session overall.