I went for a swim in Crouch End twice in the last week, first in the Lido to check if the outdoor pool had improved from last year, and secondly to use the indoor pool.
The outdoor pool was dirty because it was windy so there were many leaves floating on the surface (maybe we can pretend it's some kind of spa mud treatment?), the lawn was full of litter and the kids and teenagers were screaming, diving and splashing each other. Not my idea of a relaxing Sunday afternoon. Closing time is 7pm, my friend and I arrived at 4.30pm and most of the people were still there by 6.30, we were hoping it would get quieter after 5pm. The good thing of arriving late afternoon is that you pay a concessionary rate instead of full price.
The indoor pool was much better, the place looked clean. The pool was full of school kids so I recommend you check the online timetable, for example I went on Wednesday at 11am but at that time schoo children are using half of the pool until 12pm when the pool is then available for adults using 3 lanes for different swimming speeds.
A word of warning: many lockers are still broken from last year so you may not find a spare one at busy times to store your valuables. Bring your own towel and toiletries.