NO ONE will tell you that you should attempt an open-water swim on a whim. Indeed, Penny Lee Dean, who holds the women's record for swimming the English Channel, planned to enter the event for 13 years before actually doing it. (The planning paid off: She finished in 7 hours 40 minutes.) Of course, most swimmers interested in trying an open-water race aren't quite so ambitious -- or intrepid. Dean casually lists "ship traffic" among the event's challenges.

Whether dodging tankers or other swimmers' elbows, it takes dedication and training to complete a competitive open-water swim. If you're already a competent pool swimmer, it can take anywhere from four to six months to build the confidence that it takes to complete a race. If you're a beginner, you're looking at 2004.

"You have to be in condition." says Lynn Hazlewood, a member of the Reston Masters Swim Team and meet director for the Jim McDonnell Memorial Lake Swim. The one- and two-mile Reston races, held in late May, mark the start of the open-water season in the area. "Get used to long distances first," Hazlewood advises. "Get to know what it feels like to swim a mile."

One of the most effective ways to do that is to join a Masters swimming team. United States Masters Swimming, which has more than 40,000 members nationwide, is a coached swimming program open to anyone 19 or older. Regional divisions called Local Masters Swimming Committees are composed of the teams in designated areas. (The Potomac Valley LMSC, for example, is responsible for clubs in the District, Montgomery and Prince George's counties, Arlington and Fairfax counties and the cities of Alexandria, Fairfax and Falls Church.)

"You can swim by yourself, but you won't achieve the same level of fitness that you will swimming with a group," says Harry DeLong, head coach of the Masters team at Chinn Aquatic and Fitness Center in Woodbridge. DeLong says that structured practices, workouts that progress over time and technique improvement are what people should look for from Masters programs. "Out in the open water you want to be as technically proficient as you can be," he says.

Joining Masters also increases your opportunities to compete: Most, but not all, open-water races are sanctioned by USMS, which means that you must be a member to participate. (Its members are covered by the organization's accident and liability insurance at USMS-sanctioned workouts and competitions.) Membership in USMS costs $28 a year, while facility fees vary widely from team to team.

The chance to ditch a shared lane in an indoor pool for a vast expanse of chlorine-free water under the open sky draws many people to the sport. "It's a change of scenery," says Lora Strine of Arlington, a coach for the National Capital YMCA Masters team. "When people run, they run in their neighborhood or in a park. When you swim in a pool it's just up and back, up and back, up and back."

Not so in open water. In addition to jellyfish, frigid water, waves, currents and the flailing limbs of other swimmers, open-water racers must compensate for a lack of visibility. (Turns out those monotonous lane lines also tell you where you're going.) "When you're used to swimming in a pool those lakes can seem pretty big," says Steve Olson of Bethesda, a swimmer with Capitol Sea Devils Masters. "It's like going for a walk in a place you've never been before -- except the walk is underwater."

It's such rigors that draw people in -- and keep them there. "Sometimes you just really want to focus on something," says marathon swimmer Andrew Johnson of Arlington.

Johnson, who became a Masters swimmer in 1995 when he was pushing 30 and out of shape, swam the 24-mile Tampa Bay Marathon in 2001 and the 28.5-mile Manhattan Island Marathon last year. (He plans to swim the 20.5-mile Catalina Channel this year, and the 21-mile English Channel in 2004.) As Johnson tells it, he got into the pool and one thing led to another. "Before long I was sleeping in my Blazer like a beach bum, chasing races all over New York, New Jersey, Maryland and Virginia," he says.

"At that point I was pretty sure I was addicted to the sport."

RECOMMENDED READING

Penny Lee Dean, "Open Water Swimming: A Complete Guide for Distance Swimmers and Triathletes" (Human Kinetics, 1998). The champion swimmer writes about the lure of the open water and discusses practicalities, including gear, training and tactics.

LOCAL MASTERS PROGRAMS

POTOMAC VALLEY LMSC is responsible for the District, Montgomery and Prince George's counties, Arlington and Fairfax counties and the cities of Alexandria, Fairfax and Falls Church. www.pvmasters.org. E-mail Jeff Roddin, jroddin@pvmasters.org.

VIRGINIA LMSC includes the rest of the state of Virginia and parts of West Virginia. www.vaswim.org. E-mail Dee DeLong, deedelong@comcast.net.

MARYLAND LMSC includes the rest of the state of Maryland. maryland.usms.org. E-mail Barbara Protzman, swimbarb@hotmail.com.

UPCOMING OPEN-WATER SWIMS IN THE AREA

All of the events below have been confirmed, but the details for many have not been finalized. Races are USMS-sanctioned unless otherwise noted:

MAY 25 -- Jim McDonnell Memorial Lake Swim, Lake Audubon, Reston. One- and two-mile lake swims. 703-845-7946. www.restonmasters.org. E-mail Lynn Hazlewood, lynhzlwd@usms.org, or Gordon Gerson, usna58@comcast.net. $30, $40 after May 19.

MAY 31 -- Potomac River Swim for the Environment, Point Lookout State Park, Scotland, Md. 7.5-mile swim across the mouth of the Potomac River between Virginia and Maryland. www.crosslink.net/~ cherylw/pr2003i.htm. E-mail Cheryl Wagner, cherylw@crosslink.net. $75; swimmers also required to raise a minimum of $250 in pledges (proceeds benefit river restoration projects). Open to all.

JUNE 8 -- Great Chesapeake Bay Swim, Hemingway's Beach, Bay Bridge Marina. 4.4-mile swim. 856-468-0010. www.lin-mark.com. Online registration for this event is already closed; information about being wait-listed will be posted shortly on the event site. Requirements: Completion of a one-mile swim or longer in open water at a pace of 40 minutes or better per mile in the last two years, or completion of a continuous three-mile pool swim in 2 hours 15 minutes or better in the last two years. $150 (proceeds benefit the March of Dimes and other charities).

JUNE 8 -- Chesapeake Challenge, Hemingway's Beach, Bay Bridge Marina. 1.1-mile swim. 856-468-0010. www.lin-mark.com. Open to all. $40.

JUNE 14 -- Jack King 1-Mile Ocean Swim, Virginia Beach. E-mail Betsy Durrant, durrant6@cox.net. Meet details will be posted at www.vaswim.org as the event date approaches.

JUNE 28 -- Swim for Life, Rolph's Wharf, Chestertown, Md. One-, two-, three-, four- and five-mile river swims. E-mail Dawson Nash, swimmerdn4321@aol.com. Open to all; swimmers must raise at least $100 in pledges (proceeds benefit people living with HIV/AIDS and the Chester River Association). Last year's brochure is on the District of Columbia Aquatics Club's Web site at www.swimdcac.org; this year's brochure will be available at the same address in late March or early April.

JULY 12 -- Two-Mile Cable USMS National Championship. Chris Green Lake, Charlottesville. E-mail Patty Powis, pmpowis@saturn.vcu.edu. Meet details will be posted at www.vaswim.org as the date of the event approaches.

SEPT. 6 -- Lake Montclair, Dumfries . One- and two-mile lake swims. E-mail Wayne White, wwhitefamily@comcast.net. Meet details will be posted at www.vaswim.org as the date of the event approaches.

SEPT. 20 -- 2003 Sunfest, Ocean City. 5K, 3K and 1K ocean swims. E-mail Ken Zuiderhof, kzuiderhof@ccboe.com. Meet details will be posted at www.mdswim.org in mid- to late summer.

Swimmers wade into the water at the start of last year's Great Chesapeake Bay Swim, which is 4.4 miles long.