I’m a writer. Or at least I’d like to think so. Lately I’m a camera assistant for National Geographic photographer Charlie Hamilton James, as well as his wife. People are usually more interested in his job than mine, keen to know what it takes to get those amazing shots.

Charlie is photographing cutthroat trout, so most mornings we set out for the Snake River in Grand Teton National Park. Our goal: to photograph otters eating cutthroat.

But first, we have to find them.

View Images An adult male otter watches us from an ice hole he was fishing. Even though the river often only freezes along the edges, otters seem to like fishing through holes in the ice.

It’s December, minus eleven. One of the most popular parts of the park is deserted. I wear layers of thermal clothing. I look like the Michelin Man. The snow comes up to my hips. If I fall over I might not be able to get up again.

We push off into the flat, dark water, dipping our paddles into silent depths.

The job of a camera assistant is the job of the unsung hero, in my case a labor of love. But the physical toil is worth it for these moments—the mountains, the ice crystals sparkling through the air, and the sense of adventure. Who knows what we might see?

Some days we spend hours freezing, only to haul out of the water with the camera still in its bag. Usually we spot beavers, moose, once even an ethereal ermine, but today, within minutes, we discover wavering lines of footprints running along the bank, in and out of the water. Otter prints. Downstream a bald eagle picks up scarlet scraps of fish from the white bank. Fresh otter leftovers.

View Images Otters will run and then slide on the ice, using their bellies as sleds. It may look fun, but it’s probably just a more efficient way of traveling across snow and ice.

We paddle in silence.

Rounding a fast-flowing bend, I glance up a side stream and see an otter pop its head through a hole in the ice.

Behind me, Charlie stops paddling to reach for his kit bag. He saw it too.

I feel the current lift the back of the canoe.

“OK, you’re in charge,” he says. “Don’t steer straight at them, but we aren’t trying to sneak up on them either.”

Steering? I’m just trying to keep us afloat. I have to paddle hard to fight the river, which is determined to turn us.

More otters stick their heads out of holes in the ice.

“No, don’t turn us,” Charlie snaps. “I need to be at 180 degrees; I need to be straight on.”

Photographers aren’t like the rest of us, not when they get into “the zone.” One minute they may be a nice, mild-mannered husband and the next a different person, oblivious of anything. The subject holds their full attention; anything else is, at best, an irritation.

I keep quiet, paddling with gritted teeth.

View Images Otters will spend a lot of time rolling and sliding in the snow. This serves to keep their dense coats in good condition—but could also be fun.

Slowly I win the battle with the current. I pull us out of the main channel. Now, instead of being pushed downstream, we’re fast approaching the side of the river where ice intrudes onto the water.

“Go slowly now.” Charlie has his eyes screwed up to the lens.

There is no brake. We hit the ice with a crunch that nearly lurches him into the water. All the otters look up.

‘”What are you doing? I’m holding a camera here. Try to keep us still.”

How do I keep us still? We’re already slipping. I look down and see that the water is too deep to wedge my paddle onto the river bed.

“Get down, you’re in my shot.”

I bend double—we didn’t come all this way to have a shot of the back of my head. We’re still slipping.

Glancing sideways, I make out a hole in the ice. I stick my arm out. My shoulder threatens to dislocate, but I can just reach it. I slip my fingers in, gaining some purchase. The front of the canoe embeds a little. The current knows I’m winning and releases its hold.

“Stop moving!”

I reach out my other arm and slowly scrape a hole in the ice with my fingers.

“Keep your head down.”

I stare at the bottom of the canoe. It’s all I can see from this position. My back hurts.

“Right, I’m on a very long lens—I can’t see what’s going on. Tell me which hole they’re popping up from.”

Keeping a tight hold of my icy anchor holes, I force my head back. I can just see the ice over the top of the canoe.

View Images An otter eats a cutthroat trout. Although the Snake River contains large quantities of fish, including mountain whitefish and suckers, cutthroat trout are a favorite, as they have a higher fat content than the other fish.

An otter pops up right in front of us.

“Twelve o’clock,” I whisper. “Three o’clock. Oh gosh! Two at nine o’clock.” And that’s how it goes. Suddenly, it’s like a game of Whack-A-Mole with otters. They have holes all over the ice and dive through them, leaving us to guess which one they’ll pop up through next. I count six otters—or is it seven? They don’t stop moving; it’s hard to tell.

The gloves that Charlie had led me to believe were waterproof are not. Icy, numbing water seeps in.

I’m the most uncomfortable I’ve ever been, yet I can’t move. We’ve never been so lucky, and we may never be again.

The otters are fishing. Two haul fat fish onto the ice to eat. I pray they’re cutthroat trout. Even as they chew, they growl a warning at the others, explaining in no uncertain terms that they aren’t prepared to share.

I hear a whisper above us, and craning my head I see the bald eagle swooping hopefully.

“Bald eagle above.”

The otters aren’t sharing with him either. Hungry, he perches in a nearby tree.

My hands are numb, my neck is possibly broken, my toes are icicles, and my back is crippling, but I don’t care. My anchor system is working.

Full of fish, the otters decide to check us out.

Four otters all try to jam their heads through the tiny hole at 12 o’clock at exactly the same time. They decide we’re boring and play, rolling and chasing. They run and lift up their feet, sledging on fat bellies over the ice, then gather together in a loving family heap.

Behind me the camera streams a noise of satisfied clicks.

“This is the best otter day ever.”

View Images Philippa navigates the canoe through the Snake River.

Charlie Hamilton James was one of six photographers assigned to cover the story of Yellowstone National Park and its surroundings for the May 2016 issue of National Geographic. Have a question for Hamilton James? On Thursday, April 14, at 1 pm ET, Charlie will be live on Twitter discussing his work in Yellowstone and beyond. Tweet your questions to @CHamiltonJames using #NatGeoLive. You can see more of his wildlife photographs here.