I spent the winter training at a deep pool with gutterless sides and all lane ropes in place. Now I’m training at a shallower pool with normal sides and only two lane ropes dividing the pool into 3 blocks of 2 lanes (and they’re rarely tensioned properly). I notice a difference of 3-4s/100m. I suspect that the lane ropes are a bigger factor than the sides or the depth. Sometimes it feels like one of those amusement park wave pools… especially when there’s a water (buffalo) aerobics class sharing the pool.