“People with diabetes who take insulin or sulfonylureas like glipizide or glyburide are at increased risk of hypoglycemia, which can be dangerous in water due to sudden disorientation, fatigue, or loss of consciousness,” says Dr. Cutler. He adds that people who manage their diabetes with diet, metformin, or other non-hypoglycemic drugs face far lower risks of hypoglycemia.

The act of swimming — both the fatigue of exercise and being immersed in water — can mask the symptoms of hypoglycemia, and swimmers with diabetes should take special precautions.

• Check your blood glucose regularly. Mizokami-Stout recommends checking it every 30 minutes before, during, and up to several hours after swimming. That may mean taking breaks to get out of the pool and use a glucose meter or dry your hands to check your continuous glucose monitor readings on your smartphone.
• Start your swim with your blood sugar a bit higher than usual. This is particularly important if you know you tend to go low during exercise. You can also plan to consume carbohydrates midway through your swimming session.
• Adjust your insulin dosing. If you use insulin, you may need to lower your medication doses before, during, or after swimming to avoid hypoglycemia, due to increased insulin sensitivity, says Mizokami-Stout. If your insulin pump is waterproof and can stay attached during your exercise, you may want to set a temporary lower basal rate or use “exercise mode.”
• Keep fast-acting carbohydrates on hand. “For longer swims or individuals who are particularly prone to hypoglycemia, keep short-acting carbohydrates nearby for treatment of low blood sugars,” says Mizokami-Stout. Cutler says to keep juice or glucose tablets in your pool or beach bag, in case you need them quickly.
• Let the lifeguard know that you have diabetes. That way, they can keep an eye on you. A medical alert bracelet is another way to let people know about your health condition. If you experience hypoglycemia and can’t treat yourself, you’ll get the care you need far more quickly if paramedics know you have diabetes.
• Avoid swimming at peak insulin times. “Rapid insulin typically peaks one to two hours after injection — this is the riskiest time to exercise,” Cutler says.

To help make swimming a regular exercise habit, you need to be clear about the capabilities of your electronic diabetes devices. The leading continuous glucose monitors (CGMs) are water-resistant, but you should check your own device for specifics.

“Swimming with CGMs is generally safe, but there are a few important considerations to ensure optimal use,” Mizokami-Stout says. For starters, water may reduce the adhesiveness of the CGM sensor, requiring additional adhesives, overlap patches, or arm bands to keep the device secured, she says.

“If insulin delivery is stopped too long, some individuals with diabetes, particularly those with type 1 diabetes, may develop dangerously high blood glucose levels or a condition called ketoacidosis due to the prolonged lack of insulin,” Mizokami-Stout says. For this reason, she suggests reconnecting to your pump once hourly during longer swims to deliver a bolus.

If you use an insulin pump, you should discuss your options with your healthcare provider before starting a new swimming exercise routine.

Swimming in open water, such as in the ocean, lakes, or any body of water where you can stray far from shore, requires extreme caution for anyone, but diabetes makes it even more risky. Hypoglycemia or ketoacidosis in that circumstance could quickly become a life-threatening situation.

Stick to areas where there’s a lifeguard on duty who knows your health situation. Cutler also recommends swimming with a partner. Do your best to stay within sight of the shoreline and consider carrying your medication and quick-acting carbs in a waterproof pack that you keep with you.

• Swimming is full-body cardiovascular exercise that burns calories and builds muscle. For those with diabetes, it can also help control blood sugar and reduce the risk of complications like diabetic retinopathy and heart disease.
• People with diabetes have unique risks while swimming. Hypoglycemia, also known as low blood sugar, can be a drowning hazard. Check your blood glucose regularly, keep fast-acting carbs on hand, and let the lifeguard know you have diabetes — all of which can help you stay safer in the water.
• If you use insulin or wear a continuous glucose monitor, read and understand the instructions for your devices, so you know if and how they can be safely used in the water.