Sometime Saturday night, guided by starlight and the phosphorescence of the surf on Lake Superior, a beaver swam across nearly ninety yards of roiled water and swift spring current at the mouth of the Amnicon River.  The animal hauled his bulky body, thick fur slicked back and shiny with water, up onto the narrow spit of sand and gravel that fingers between the river and the gaping emptiness of the big lake.  The flat weight of his tail -- fully ten pounds or more -- furrowed the sand behind him like a rudder carves through water.

As soon as he'd climbed to the highest, driest ridge on the sand bar, the beaver turned his back to the winking lights of Duluth and headed east.  Although beavers are strong swimmers and surprisingly agile in water, on land their movements are slow and plodding.  Their short legs and huge, webbed feet, which serve so well to propel their smooth bodies through the heaviest current, produce an ungainly land gait that is more like a waddle than a stride.  And that tail, its weight nearly a quarter of the creature's entire body mass: on land it's nothing but dead weight, as if a person were to drag a thirty pound log behind him.

The beaver's progress along the beach, measured by a stride not much longer than the length of those enormous, three-toed hind feet, was slow but steady.  The animal neither paused nor hesitated: doggedly he soldiered through the loose, shifting sand, the rhythm of his gait swinging his body in gentle S curves as his rear end shifted in one direction and the tail responded with a countermarch.

The beaver was a large one, fully mature, forty or maybe fifty pounds: big and experienced enough to recognize the authority that comes with size -- a predator, even a wolf or a bear, would think twice before challenging a full grown beaver with its razor sharp teeth and powerful claws -- but also acknowledge his vulnerability as an animal removed from its natural habitat.   A beaver seldom travels any appreciable distance on land.

The surface of the lake glowed under the weak light of the stars: the waning crescent of the moon would not rise for another hour.  The surf churned heavily, driven by a strong wind that during the day had led from the south but with dusk now whipped waves across the geographic thickness of the lake in corrugated ridges that foamed with the red mud of the iron range.  The beaver heard the sighing of the surf beneath of the wheeze of his own heavy breaths.  Deliberately, he detoured down from the soft, slinky sand of the ridge, pockmarked by the footprints of a hundred happy humans who had romped along this beach with their dogs and their kids and their shouts on this first warm weekend day of spring.  The beaver trailed his tail through the line of debris that marks the ever-changing boundary of the lake.  In the firm, wet sand, his hind paws left their unmistakable imprints: a slim, elongated heel topped by three long toes connected by webbing and crowned by thick, curved claws.

The beaver made no effort to avoid the water of a shallow spring rivulet: he ploughed forward without breaking stride and then weaseled through a tangled mass of driftwood logs and back up to the dry sand ridge.  He'd been walking on the open beach for over an hour: he was now almost a mile distant from where he'd begun his trek at the mouth of the sweeping, brown river.  During his time on the beach, he had encountered no other living creature: not a fox, not a mouse, not a goose or a crow or a gull.  Everything seems to be sleeping tonight, exhausted by the excess of early spring, or perhaps hunkered down in anticipation of the changing wind.

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Likewise, no human marked the passage of the one lone beaver along Saturday's starlit beach.  I discovered the trail the beaver had left after the fact, in the dim light of Sunday's dawn.  At first, I was completely baffled: the size and depth of the individual paw prints pointed to a large animal but the prints were too indistinct to read details.  The abbreviated distance between the tracks completely confused me: no bear or canine has a stride that short.  I followed the trail for several hundred yards before I discovered a clear imprint -- left when the animal forged through that seasonal creek -- and was then able to positively identify the walker.

But with that identification came questions.  Why did the beaver choose to walk along the beach instead of swimming, his preferred mode of locomotion?  That answer was easy: the surf of the lake was heavy that night, with four and even five foot waves crashing into the beach and flinging logs like matchsticks.  A beaver is no fool, especially one this old and experienced: he knew that surf, driftwood, and the shifting currents of the inflowing river produce a dangerous aquatic environment, even for one accustomed to life underwater.  The big lake that night was nothing that he was willing to hazard, even if the alternative was a couple of hours of awkward walking.

Where was the beaver headed?  Another question that was easily answered.  I followed the trail of beaver tracks and the S shaped sweep left by his tail to the next drainage east of the Amnicon: Hansom Creek.  At the stagnant pool at the edge of the beach, the line of beaver tracks slurped down into the muddy brown water and disappeared.

Which led to the final, most important question: why?  Why did the beaver leave the mouth of the Amnicon River and plod over a mile across the uncertain sand just to get to another stream?  As I backtracked along the beaver's trail, I speculated.  I remembered that for a couple of days I'd heard the slap of a beaver's tail when I approached a particular grove of aspens near the mouth of the river.  Had this beaver attempted to set up residence near the aspens but become disgruntled by the human traffic in the area?  Had he lost his mate during the winter and set off to new territory to look for female companionship?  Had he sensed in the changing wind Sunday's hard rain that ended up flooding the river and probably washing out his home?

Unlike many people, I've never been a big fan of mystery novels.  Their human-centered plots always seem a bit contrived, their resolutions a little too pat.  I can find more mystery than I can handle during my daily walks along the beach, mysteries rife with complications and intricacies that I know will be impossible for me to ever completely resolve.