It's hard to imagine a nicer way to spend a fall Sunday morning than canoeing through the backwaters of the Pohick Bay Regional Park. This wonderful adventure is now an educational -- and inexpensive -- reality made possible by the Northern Virginia Regional Park Authority in its fifth annual fall series of half-day canoe trips.

Although eight o'clock in the morning appears to be an outlandish time to begin anything on a weekend, it's a good time to open your eyes to Mother Nature in one of her finer hours. Geese, ducks and other waterfowl -- not to mention bald and golden eagles -- can be seen soaring overhead.

The series, which runs through October 10 (more trips may be added, depending on demand) costs a mere $10 with all canoe equipment included. The real bonus of the nearly four-hour aquatic tour is having a Park Authority naturalist like Earl Hodnett to guide the beginning canoeist through the paddle-by-paddle process, explaining the hows and whys of marsh life.

Hodnett, chief naturalist at the park authority, and assistant Marta Sylvester, explain the simple operation of the canoe and then guide the group of 18 or fewer through a small portion of Pohick Bay and into the freshwater marshlands that border the 500- acre Mason Neck park.

Several times during the trek, the canoes stop and pull together around the naturalist, who's likely to explain not only the marshland vegetation but also the behavior patterns of local critters. Spatterdock, wild rice, and pioneer trees share the limelight with beaver, raccoon, fox and whitetail deer. Pelts of mink, muskrat and even the shell of a snapping turtle are passed from boat to boat for the layman's examination.

Plant and animal life are directly affected by underwater topography. The changing currents of the bay's tidal waters, the inlet at Gunston Cove and the Potomac help shape the evolution of water life.

Most places, the water's no deeper than six feet and when the carp aren't spawning it's clear enough in the back marshes to see bottom, a rarity in today's waterways.

A bag lunch and beverage will top off the morning when you make a final stop at the base of an easily climbed cliff. At the top, there's a splendid view of Pohick Bay and the Potomac in the distance.

The trip is very relaxed. "It was nice and informal," said Pat Canby after her first attempt at canoeing. Her friend, Carl Noller, was back for the second time. "It's like having your cake and eating it too," he said.

One thing the expedition is missing is bugs. On a recent trip, not one of the pesky devils was seen or swatted. KEEN AND BRIGHT PADDLING For information on the "Canoe the Marsh" series or on the October 24 "Fall Colors Cruise," call the Northern Virginia Regional Park Authority, 278-8880. SOONER BUT FARTHER The Maryland Forest & Park Service is offering a one-day canoe trip through Pocomoke River State Park on the lower Eastern Shore, October 2. The 101/2-mile trip, including all canoeing equipment and lunch, costs $20. Also planned is a three-day canoe trip down the Potomac, October 16-18 for $55. For information call 301/269-3771.