NOAA 99-R133
Contact: Gordon Helm


As hundreds of swimmers participate in the 4.4 mile Great Chesapeake Bay Swim for the March of Dimes on June 13, information collected by the National Oceanic and Atmospheric Administration about weather, water temperature, tides and currents will help them meet the challenge more safely and assess the risks of the open-water swim.

Race organizers will use the NOAA information to confirm or adjust the early morning start time based on actual currents and weather conditions Sunday morning. Swimmers and organizers will have the latest information on currents, wind, or any potential storms to help make the open-water swim as safe as possible.

The annual Great Chesapeake Swim has drawn more than 600 swimmers in past years. Participants attempt to cross the Bay from Sandy Point State Park on the west bank to Kent Island on Maryland's Eastern Shore, swimming between the spans of the Bay Bridge.

Since NOAA began providing advice on tidal currents for the race in 1993, swimmers have not had to contend with strong tidal currents like those experienced in 1991 and 1992. Only a few dozen of the approximately 550-600 swimmers per year were unable to complete the race between 1993 and 1997, when NOAA assisted with the timing of the start of the race. In 1998, only eight swimmers out of 549 starters were unable to finish the race, which was run under favorable conditions.

Of concern at this year's swim could be the early arrival of sea nettles. Fresh water runoff into the Bay was recently reported by the United States Geodetic Survey as below average for the last 10 months. Salinity levels in the Bay waters are higher than usual as a result and could increase the abundance of jellyfish farther up the Bay.

NOAA's National Ocean Service has predicted slack current conditions at Sandy Point at about 7:20 a.m., the tentative race start time. Slack tide occurs when the tidal current switches direction, resulting in the slowest current speeds. The current will be switching direction from a flood to an ebb current over the course of the race. Most swimmers will be in the water traveling with the slack water as it crosses the Bay during the tide change. Some of the faster swimmers will feel the decreasing flood current and some of the slower swimmers will feel the increasing ebb current.

NOAA's Chesapeake Bay Office is coordinating the agency information for the swimmers and race staff. In addition, this year NOAA Chesapeake Bay Office personnel, with the support from Maryland Department of Natural Resources' Research Vessel Discovery and University of Maryland scientists, will be conducting research cruises on June 11 measuring real-time current velocities by towing an Acoustic Doppler Current Profiler (ADCP). NOAA towed an ADCP in past years and observed the pattern of currents between Sandy Point and Kent Island during the part of the tidal cycle when the swim would be taking place. NOAA has found consistent patterns of slack tide every year, with the current changing direction on the Sandy Point shoreline first and the majority of the swimmers traveling with the slack current as it moves eastward.

The NOAA Chesapeake Bay Office coordinates NOAA's Chesapeake Bay efforts with the multi-state/federal partnership known as the Chesapeake Bay Program, working to protect and restore the Chesapeake Bay. The NOAA Office will have a booth set up at the finish line to distribute information on Bay tides, currents, weather and efforts to restore the Bay.