The Winter Season Nobody Outside the Trade Knows About

By Ray Whitfield, ADCI-certified commercial dive supervisor. Reviewed by Dana Whitcombe, technical reviewer.

Cathodic Protection & Anodes | Offshore & Subsea Diving January 8, 2020. The intake at a 60-year-old hydro plant in upstate New York was 40% plugged with ice and debris. I was dive supervisor for a three-man crew sent to clear it. The air was 14°F, and the water ran at 38°F. My diver looked up from his hard hat and said, 'My last job was in the Gulf. I wore a t-shirt.' He went in wearing a hot water suit fed by a surface heater. If that heater failed, he had maybe three minutes before his core temperature started heading down. Nobody outside this trade knows that winter is when we do some of our most critical work. The stereotype of commercial diving is warm water, sun, and oil rigs. But inland and industrial diving—dams, bridges, water tanks, power plant intakes—runs on a different calendar. Winter isn't a closed season. It's often the season. Ice blocks trash racks. Intake screens clog. Facilities call you when a plant operator hears an unusual cavitation and prays it's not the beginning of a catastrophic failure. And the cold changes everything about how you plan, gear up, and dive.

Why Winter Is a Busy Season

When the leaves fall and the water goes hard, most people assume dive jobs shut down. For us, it's the opposite. Power plants run at peak load when the grid demands heat. Dams have to manage ice that can jam gates and damage penstocks. Water tanks still need inspections, and in many areas you can work on them with less impact because municipal demand is lower. Plus, some rivers drop in winter, exposing structures that are hidden the rest of the year. That's when you can finally replace a corroded anchor bolt on a spillway that's been on the list since August. So the phone rings more in January than June.

The Cold Is a Different Element

Water at 38°F doesn't feel like air at 38°F. It feels like a physical weight. Cold water pulls heat away from your body far faster than air ever can, and it doesn't care how tough you are. That's why we use dry suits or hot water suits. The hot water suit is a closed system: a boiler on the surface heats water, pumps it down the umbilical, and circulates it through small tubes in the suit. It works beautifully, right up until it stops. We practice that failure. We've all felt that first chill when the heater hiccups, and you know you have seconds to decide whether surface immediately or risk a rapid core drop. The cold also lies. Your dexterity goes before you notice, and your brain gets foggy. That's why we have a hard rule: in cold water, you have a tender whose only job is to watch you and talk to you every thirty seconds. If you stop answering, you come up.

Gear Gets Rigged for Frost

Setting up a dive site in winter is half the job. Compressor filters need preheating or they freeze and pass moisture into the air. Hoses lay on snow and turn stiff as rebar. Umbilicals can kink. The dive hole itself has to be chopped through ice, and you have to keep it open with an aerator or a pump, because ice will close around your umbilical and pinch it. Your tenders are in heavy coats, gloves, and waterproof boots, and they're the ones who handle the ropes and hoses. They don't get to wear a hot water suit, so you have to rotate them often or they'll go numb too. And then there's the comms. Freezing fog on a microphone can make you sound like you're underwater, which is exactly when you can't afford to be misheard.

The Plan Is Different in Winter

Every dive plan, wet or dry, starts with a hazard assessment. In winter, that assessment has its own section. We check for current, ice, entanglement, and overhead hazards. But winter adds a whole category: thermal. We set time limits based on water temperature, not just depth and decompression. We have a heated shelter on site for the diver coming out. We have a hypothermia protocol, and we bring extra blankets and a warm drink that doesn't contain caffeine, because caffeine isn't your friend when you're trying to rewarm safely. We also talk about the intake. If a trash rack is partially clogged, the suction can pull a diver against it. In cold water, panic uses up oxygen fast, and you don't have oxygen to waste. So we plan for it, we walk the diver through it, and we have a dedicated standby diver ready to go in if the primary gets in trouble. Nobody does that for a warm-water dive.

What Outsiders Don't See

I've had strangers at a bar say, 'You're a diver? Must be nice and warm down there.' I laugh and say, 'It's about as warm as a fridge, and the fridge is vibrating.' But there's a seriousness they miss. Winter diving isn't an adventure. It's a job. It's a job where the client is a utility manager who's on the phone with the mayor because a neighborhood might lose heat. It's a job where you show up to a frozen reservoir, cut a square hole, and send a human being down to fix a valve that controls drinking water for a town. The reward isn't a tan. It's a functioning utility and a crew that drives home with fingers intact. That's what the winter season is about.

Frequently Asked Questions

How cold is the water when you dive in winter? Typically between 32°F and 40°F. It's liquid because it's moving, but it's still cold enough to cause hypothermia within minutes if you're not protected. Do you actually dive under ice? Yes. We cut a triangular or rectangular hole in the ice and use it as the entry point. The ice makes a solid surface, but we keep a tender on the line and clear the hole as it freezes. What happens if your hot water suit heater fails? You surface immediately. It's a rehearsed emergency. A hot water suit failure in cold water is not something you ride out. You get out, and you get warm.