In Alaska's Katmai National Park and Preserve, I hiked through woods dense with spruce, willow and balsam poplar trees. Wildflowers dotted the ground amid stretches of spongy tundra, meadows and marshes. The air, cool and moist, seemed like the cleanest on the planet. Breathe deeply, I thought. Take it in. But be vigilant.

About a mile from my lodge, a gate led to an elevated walkway. In another 50 yards, a second gate — more like a door, 6 to 7 feet tall and reinforced with metal — bore a sign: "Keep door closed."

I slipped through, carefully closing the door behind me, and heard my feet echoing on the wooden planks as my pace quickened in anticipation. Soon I heard the steady roar of Brooks Falls. Then I spotted them: lumbering brown shapes of grizzly bears in the Brooks River above and below the falls. They were huge — and they were the reason I had come.

I had wanted to visit Katmai for years, ever since I had read that visitors can see and photograph grizzly bears feasting on salmon at the falls.

The park is home to an estimated 2,200 grizzlies. One of the largest bears in the world, they can measure 7 to 10 feet long and weigh 1,000 pounds or more. Brooks Camp, where I stayed inside the park, hosts one of the world's highest densities of grizzlies.

I went in July, when salmon return to their home stream to spawn and as many as 60 bears congregate along a half-mile stretch of the Brooks River to fish.

Catching a salmon at Brooks Falls.

From late June through July, hundreds of thousands of salmon swim from the northern Pacific Ocean up the Brooks River, fighting their way upriver. Brooks Falls acts like a hurdle in their path, and the fish fly out of the water, making desperate leaps to reach the top of the falls.

That's where many grizzlies hang out to feed on the salmon, fattening up for a five- to seven-month hibernation.

I witnessed this force of nature after arriving on a 10-passenger seaplane from King Salmon, Alaska. Before I could set foot in the park, I joined other newly arrived visitors at "bear school" in the visitor center.

A National Park Service ranger explained park rules about keeping food in a special bear-proof locker and shared advice about attending to backpacks and other belongings, or they might become playthings for curious bears. Gated walkways and bridges were designed to protect visitors.

Mostly, the ranger prepared us for possible bear encounters. The key is to avoid surprising a bear, she stressed. Make noise. Talk, sing, whistle, hike in groups and stay alert, she advised. If you see a bear, keep your distance — at least 50 yards, or half a football field. If a bear changes its behavior in any way in response to your presence, you are too close. Back off. If you encounter a bear on the trail, do not panic, the ranger said to nervous laughs from the visitors. Talk to the bear in a calm but firm voice. Do not run. Do not make direct eye contact.

"I talk very softly and say something like 'Hello, Mr. Bear,' or 'Hello, Mr. Brown. How are you today?' " the ranger explained. "Then I step aside to let the bear pass."

Days of watching bears

I spent three days at Brooks Lodge, making the 1.2-mile trek from the lodge to the park's three bear-viewing platforms every day after breakfast, returning to the dining hall for lunch, then hiking back to the falls and staying until dinnertime. Park rangers were almost always around to serve as ambassadors for the bears.

On a couple of afternoons, I encountered what they called a "bear jam." Rangers had spotted bears along the Brooks River near the gated footbridge leading to the viewing platforms. Visitors heading there had to wait until the bears were at least 50 yards away.

One morning, as I began the trek from my cabin to the viewing platform at the falls, other hikers and I were stopped again.

"We have bears sleeping along the trail," a ranger explained. Shortly afterward, the sleeping bears dispersed, and we got the all-clear.

During my visit in July, the viewing platform at the falls was packed, especially at midday, when day-trippers fly in for the afternoon. Fortunately, the park rangers have a system: They count the number of people on each platform — the platform at the falls has a 40-person capacity — and create a waiting list when the space is filled. Visitors are limited to an hour on the platform. When they yield their spot, they can put their name on the list to return later.

I watched so often and closely that I began to recognize individual bears and their fishing techniques. The larger, more experienced bears perched at the top of the falls and waited. This technique requires a combination of patience and precise timing, as fish make a mad leap to the top of the falls. Sometimes, fish seem to practically jump into a bear's mouth, but that doesn't mean catching them is easy. The fish are squirmy, strong and slippery.

Some bears stood or sat in the foamy area at the base of the falls, waiting for prey. Others were snorkelers, sticking their heads underwater to find fish. Younger bears sometimes chased fish through the shallows.

When they caught fish, some bears devoured them on the spot, while others carried their catch at least a few yards away. One bear brought his salmon to a large rock in the water, using the flat top of the boulder as a table for his meal.

The 4- to 6-year-old bears (the rangers call them "subadults") often stood on their hind legs or perched on rocks to survey the water. When they caught fish, they made a beeline for the river's edge or hustled under the viewing platform with their prize, seemingly afraid of having it snatched away. Always waiting in the wings were seagulls, which cleaned up the leftovers. Bald eagles often watched from perches in trees along the river.

Brooks Lodge

I stayed at Brooks Lodge, a rustic, comfortable place to sleep, eat and meet fellow travelers. Its 16 homey cabins, outfitted with bunk beds, were built in the 1960s. The Brooks Lodge dining hall serves excellent buffet-style breakfasts, lunches and dinners. Some guests said they couldn't stomach salmon after watching the bears gorge on it all day, but I indulged for dinner every night.

I never ran into a bear during my twice-daily treks, usually solo, to and from the viewing platforms. Other visitors did, though, encountering subadults chasing each other through the woods, a large loner or a mother and her cubs.

On my last day at Brooks Lodge, I saw a mother with cubs, too. At the falls, I smiled to see familiar bears. Then, on the far side of the river, I spotted a small bear with three cubs I hadn't seen before. They looked tentative and stayed only for a moment. Was Mom showing the youngsters where she and generations before them had fattened up for hibernation, where in the coming years the cubs, too, would learn to fish?

As I hiked back to the lodge to catch the floatplane out of Katmai, I realized how enchanting it had been to see that foursome. They were a reminder of how species and their cycles of life intertwine. Salmon return to their birthplace — past one of the world's largest concentrations of grizzlies. And people who time their visit right can witness the fascinating result.

Sue Kirchoff is a Minneapolis-based writer and photographer.