Hi Claire, I've just swum 84 lengths today and the way I work it is, I suspend the dosage and turn my sensor connection off. I try to get my sugars at around 9 and normally find they come down to around 6ish after the swim. All of us will differ and it all depends how hard you work on your swim as that can alter your levels quite a bit. My sugar level was 11 today but because I worked pretty hard in my swim they dropped to 6.7 which was fab. After my swim I turn my pump back on and reconnect my sensor as well as taking a blood sugar reading to help my sensor adjust if required. I'm using the Medtronic 670g pump by the way.