CAMDEN. There is always a slight foreboding as I negotiate that steep, last step down to Laite Beach.

Behind lies the civilization of warm car interior and grass embankment and asphalt pathway and picnic tables. Ahead lies sand, shells, seaweed (is it wet or dry? is the tide advancing or retreating?) and the pebbled shore.

I have come not to stroll or read, but to swim.

Some days there are reassuring signs: the sun is bright, the sand exudes warmth, the harbor is still, the water a light shade of green, and youths are sunning like seals some yards from the shore.

But on other, more somber days, the waters are a darker grey, or are wrinkled by wind, or clouds shadow the beach, which is almost deserted, and the wet margin of sand under the receding wave feels disconcertingly chill.

So I don't always end up swimming. Sometimes, after wading in up to my thighs, I decide it's just too cold for comfort, and I abandon the mission and return to shore.

But usually, as long as the water does not make the bones ache, I affix goggles to face - the gesture that signals I am determined to make the plunge - and dive forward into discomfort.

Experience has taught that the immediate, searing cold on chest and face will indeed melt into a bracing but bearable equilibrium of body and water - but only after a good half minute of gasping for breath and frenetic kicking.

The worst now past, I stand up in the shallows to adjust leaky goggles, taste again the mineral salts of the seawater, and get ready to swim.

Experience has also taught that on calm days there is a stable layer of water within a couple feet of the surface - the thermocline - that is perceptibly warmer than the water below. So I keep to this more habitable region of relative warmth - much easier in salt water than in fresh pond or lake.

But after a storm, or sometimes in an early morning rising tide, the deeper, colder waters well their way upwards, and there is no warm refuge near the surface. If I swim at all on those days it is not for long.

Once the real swimming starts, especially when doing the crawl, one's breathing is no longer second nature and no longer silent as it is on land. Instead, while facing down, it seems one is shouting out air into the water, and startling the crabs just a few feet below as they scuttle away over silent sands.
Then, every few strokes, there is the body-roll towards the sky for a precious intake of breath. Horizontal, of course, and with a shifted perspective, one glimpses the bright sky and passing buoys and mooring lines through the dripping arch of the plunging arm, and then it is face down again into the green watery world, where the mooring lines can be seen continuing down into the dark.

Here in Maine my swimming is usually solitary - though I reassure my family that I only swim alone when in waters just a few feet deep, and rarely far from shore.

But in Thailand a few years ago, for a triathlon, where hundreds rush into the water together, about halfway through the swim leg (by which time one is surrounded only by those swimming at the same pace), and a long way from shore, I found myself close by a woman in a bright orange swimsuit, and every time I rolled to my right to breathe I met her goggled face turning left to breathe, just inches from my own. Breath after breath, as we made for the shore.

When we surfaced onto dry land, she soon raced away in her bright orange suit, younger and fitter and faster.

Sometimes, when sailing, I have seen porpoises exuberantly sewing the sea beside the boat, for just a few moments before their glistening bodies disappear below the waves.

How tantalizing must be the porpoises' vision of a world beyond the surface of their own.

The seals have it better, able to pull themselves up onto the rocks, for a more leisurely view of the passing scene.

After a while, even near the surface, the cold begins to seep into the body. This is, after all, an alien element. One tires, and the primordial fear soon whispers its warning: leave these waters while you are still able.

Swim now finished - no mermaids or porpoises encountered - I exit the water, skin tightened by the cold, feeling with each sharp pebble the returning weight of the vertical life.

Also feeling - the cliché is apt - more alive.

Stephen Harder is a resident of Rockport, living and working in China, and home for the summer.