The GCBS is a charitable fundraiser for the Central Maryland Chapter of the March of Dimes. The net proceeds of the event go to aid the March of Dimes in its Campaign for Healthier Babies. The 1991 Bay Swim had 844 participants -- a stunning growth from it's annual participation of 1 swimmer (founder Brian Earley) in the early 1980s.  Unchecked, it has been estimated that the GCBS could attract 3,000 entrants annually.   Since 1993, the Coat Guard has limited participation in the GCBS to around 650 participants to ensure a safe and well-organized event (see Federal Register notices). Typically, about 650 participants start the race in two equally sized waves fifteen minutes apart, with the faster swimmers starting in the second wave. This arrangement helps to group the swimmers as much as possible during the race to assist the kayakers and boaters in monitoring and aiding the swimmers.

The GCBS requires a major commitment to proper training and open water experience. To be accepted, applicants must submit documentation that they have either completed a recent open water event or completed a three-mile pool swim in under 2 hours 15 minutes (see Lin-Mark for details). Although over seven thousand swimmers have successfully completed the event over the years, the achievement has been a once-in-a-lifetime experience for about 59 percent of the finishers. To increase safety, wetsuits are allowed and encouraged (the GCBS is not a U. S. Masters Swimming event). Among the difficulties that may be encountered during the average 2 hour 25 minute swim are flailing arms and legs during the "Cuisinart start;" cross currents; swells; chop; hypothermia if the water is cold; nettle stings if the water is warm; and collisions with the bridge supports, construction cables, or the rocks surrounding the jetties, islands, and causeways.

Since 1993, the National Oceanic and Atmospheric Administration (NOAA) has measured tidal, current and weather conditions prior to the event and compared the results with predicted conditions to determine the optimum starting time for the event. As a result, 79-99 % of the starters finished the race since the 1993 event. Prior to this, in 1991 and 1992, a strong ebb current of about 2 knots in the main channel beneath the 200-feet high spans (one and a half miles from the start) precluded all but the strongest and most determined swimmers from finishing the event (only 15-19 % finished the swim).

At its widest point, the Chesapeake Bay is 30 miles across and narrows to just four miles where it is crossed by the William Preston Lane, Jr., Memorial Bridge, built in 1952 (northern, westbound span) and in 1973 (southern, eastbound span). No one knows who was the first to swim across the bay at this point. However, a determined 21-year old, Brian J. Earley, started what is now the GCBS with his first solo swim from Kent Island to Sandy Point State Park on June 13, 1982, in memory of his father Joseph Earley, who died of diabetes complications in 1981. Two years later, race organizer Fletcher Hanks began a separate bay swim event which attracted 2 swimmers the first year and 67 (48 finishers) in 1985. On June 15, 1986, the Hanks and Earley events merged when 211 swimmers successfully swam from Westinghouse (south of the bridges on the western shore) to Hemingway’s Restaurant. The following year, the event started at Sandy Point State Park, which established its present course.  Brian Earley, originally a Chesapeake Bay area resident, has moved to San Diego, California. Nevertheless, Brian has returned the second Sunday of every June since 1982 (except for 1998 and 2004) to once again swim the Bay in honor of his father and to help those who are less fortunate.