Swimming with a pump or sensor
You cannot carry sugar into the water or check mid-length, so swimming with type 1 needs its plan made on dry land. What that plan looks like.
Swimming is the awkward one, for a reason worth naming plainly: you cannot carry sugar into the water, you cannot easily check mid-length, and a low in a pool is not like a low anywhere else. Everything about swimming with type 1 follows from those three facts rather than from anything about the kit.
- A low in water is a drowning risk, which is why the plan matters more here than for any other sport.
- Fast sugar goes poolside, and someone there needs to know it is yours and why.
- Sensors and pumps are water-resistant to a stated depth and time, which is not the same as waterproof. Check your own model.
- Pumps come off for swimming; how long that is safe for, and what to do about it, is a decision for your diabetes team.
- Steady swimming usually lowers glucose and hard sprint sets can raise it first. A hypo can come on during the swim or straight after, and again hours later or overnight.
Why a low in water is its own problem
Everywhere else, a low gives you options: you stop, you sit down, you eat something, you wait. In water you have none of those immediately. Confusion and weakness, which are ordinary hypo symptoms, are exactly the symptoms you can least afford in deep water, and the usual response of “carry on to the end and then deal with it” is genuinely dangerous rather than just unwise.
Swimming also hides the warning signs particularly well. You are already cool, already breathless, already working, and you cannot feel yourself sweating. Add that you cannot glance at a phone mid-length and you have removed most of the ways you would normally notice.
None of that is an argument against swimming, which is excellent exercise and very manageable. It is an argument for deciding the plan on dry land, once, rather than improvising it at the side of a pool.
Poolside sugar, and a person who knows
Since nothing can come in with you, fast-acting sugar lives at the end of the lane, with your towel, where you can reach it in one movement at the wall. Glucose tablets or a bottle of full-sugar drink both work; the point is that it is at the poolside and not in a locker down a corridor.
Then tell someone. A lifeguard, a coach, or whoever you are swimming with: that you have type 1, that if you look confused or stop making sense they should get you out and give you sugar, and where it is. This is the single highest-value thing on the page and it takes about fifteen seconds.
Checking before you get in is worth making automatic, and stopping at the wall to check partway through a longer swim is worth building into the session rather than treating as an interruption. Open water changes the calculation again, because there is no wall and no poolside: that needs a boat, a buddy who knows, or both, and is a conversation to have with your team before rather than after.
What water actually does to sensors and pumps
Most sensors are rated water-resistant to a stated depth for a stated time, which is a specific claim and not the same as waterproof. Check what your own model says rather than assuming, because the numbers differ. Adhesive is the more common casualty: repeated swimming loosens edges, and an overpatch or extra tape helps more than anything else. Chlorine and salt water are hard on adhesive too.
Signal is the other thing that surprises people. Water blocks the connection between a sensor and a phone or reader, so readings usually stop while you are actually swimming and catch up afterwards. That is normal, not a fault, and it is another reason the plan cannot depend on watching a number mid-session.
Pumps generally come off to swim. How long yours can safely be disconnected, and whether anything needs to happen before or after, is a decision your team makes with you, because the answer depends on your setup and it runs in the direction of ketones if it is got wrong. Where you put it while you swim matters too: a hot poolside is not kind to insulin.
What changes the plan
A short steady swim in a lifeguarded pool with a friend who knows is a very different risk from an hour of open water alone. Sprint sets behave more like other hard efforts and can push glucose up before it falls. Cold water makes you work harder than it feels like you are. And a club session where the coach knows is genuinely safer than an anonymous lane swim, which is worth factoring in when you choose where to go.
What the plan looks like
Examples, not instructions or doses.
Your glucose tablets sit on your towel at the end of your lane, not in the changing room. At the wall they are one reach away, which is the entire difference between a pause and a problem.
Thirty seconds before you get in: you have type 1, if you look confused get you out and give you the drink on the towel. Nobody makes a fuss and the gap in your plan is closed.
Your sensor goes quiet for the whole swim and then catches up in the changing room. Water blocking the signal is expected behaviour, which is why the plan was never to watch the number while swimming.