THE ONLY THING better than messing about in boats is messing about in boats in the mucky magnificence of a marsh. The recent revolution in sea kayaks has made it easier and safer than ever to explore the region's vast freshwater and saltwater marshes. And fall, with its crisp days and huge flights of migratory birds, is the best of all seasons.

Conventional canoeists generally pull out of our great rivers -- the Delaware, Patuxent, Potomac, Rappahannock, York and James -- at the fall line, where the rapids end and the marshes begin. Paddling sluggish tidewater can be a chore, and contrary winds or waves can quickly flip or swamp a high-sided open canoe. Sea kayaks, with their watertight decks, are swamp-proof and less affected by wind. These are not the tippy-dippy boats in which whitewater paddlers dance with death, they're long, broad and benign. Dozens of new models have been designed to be inherently stable even in novice hands, which makes them ideal for big waters, yet still slender and shallow-draft enough to navigate the narrow channels where nature keeps her secrets.

This goes double for the marshy margins of Chesapeake Bay, and perhaps triple for the seaward side of the Delmarva Peninsula, especially the hundreds of square miles of public marsh sheltered by the belt of barrier islands that form the Virginia Coastal Reserve.

Between the islands and the mainland of Accomack and Northhampton counties is a glorious expanse of tide-washed land that ranges from firm to jellylike, veined by shallow waters teeming with fish and fowl. Quiet, patient paddlers will be rewarded with up-close and personal encounters with such shy species as rail birds, known locally as marsh hens, which many a veteran birder has sought in vain. You may encounter raccoons and foxes making their rounds, and a whitetail deer may surprise you as it comes swimming by on its way to or from the islands. I have encountered deer placidly dog-paddling along far from the nearest land; Cork McGee, a Chincoteague waterfowl guide and decoy carver, recalls seeing deer swimming some five miles offshore.

On one of the islands, I won't say which because under Nature Conservancy rules you aren't supposed to venture beyond their beaches, you may see giant Western jackrabbits. They were imported years ago by the sort of innocent meddlers who introduced sika deer -- miniature Oriental elk that breed like rabbits -- onto Assateague Island. Assateague's habitat is under constant assault by two voracious exotic species, the other being those vicious, voracious and beloved wild ponies.

Of all the Middle Atlantic marshes, those of the Virginia coast are the most extensive, accessible and interesting. There are 30 state boat ramps and countless private ones in Accomack and Northhampton counties, and plenty of other places where sea kayaks may easily be launched. If you need to park on or cross private property, just ask; there are no friendlier or more generous people anywhere.

Along with intimate encounters with the abundant wildlife, the rewards include the occasional discovery of fascinating flotsam or jetsam. The marshes comb both treasures and trash from the sea, and you may find Japanese glass fishing floats, fish crates from Thailand, ornate aquavit bottles from the Baltic or fragments of shattered vessels that failed the test of the cruel sea. Once, when I was hunting marsh hens with guide Z.R. Lewis III, we came upon a trim little gunning boat that apparently had drifted for many days and miles. It never was claimed; whenever we use it we wonder what became of the owner.

Which introduces the subject of safety. Along with improvements in sea kayak designs have come inexpensive electronic devices that can help you stay out or get out of trouble. Cellular phones work fairly well over most of the Virginia marshes. Better yet are handy, inexpensive and waterproof Very High Frequency two-way radios, which cover the emergency marine bands monitored by the U.S. Coast Guard stations at Wachapreague and Norfolk and by watermen, fishermen and charter boat captains. Global Positioning Satellite receivers that now can be had for under $100 will record your wanderings so that you'll have an exact backtrack to follow. There are plastic-laminated maps available at most Eastern Shore marinas that include GPS coordinates, so that you can pinpoint your position within a few yards.

What's the big deal, you say, when there are plenty of landmarks to go by? The skein of channels, "guts" and creeks is so spiderweb-intricate that if you don't have a map, or lose your place on it, it's possible to paddle for hours without finding the way to a destination that is always in plain sight. And low tide may bring a double whammy: Many of the smaller channels drain dry and may strand the inattentive; the level of the water in other channels may drop so far that you can't see beyond the next bend, especially from a low-slung kayak. You don't know what alone is until you find yourself lost in the marsh on a dark and stormy night.

That's why, as with any other open-ended outdoor activity, it's best not to go alone, or too far. Modern sea kayaks have plenty of dry storage space; use it. Slather on the sunblock and pack beaucoup bug spray. Carry more clothing than you expect to need and food and water you don't expect to consume. Carry a flashlight and extra batteries for it and all your electronics. Pack emergency flares sufficient to celebrate Independence Day. And always let some sensible person ashore know where you're going and when you should be back. We have no readers to spare.