MOWSA currently offers several solo, sanctioned swims that challenge marathon swimmers over long distances in cold water.

Reverse Boston Light Swim – 8 miles (12.9 km)
M Street Beach, South Boston to Little BREWStER Island

The Boston Light Swim and the Reverse Boston Light Swim have a ton of history. The RBLS is a tide-assisted, cold water swim. It starts from M Street Beach in South Boston, winds though the Boston Harbor Islands (which is a national park) out to Boston Light on Little Brewster Island.

What to expect

Water Temperature: 58 to 68 degrees F

Tides: This swim has to be tailored to the swimmer's pace. You start at the M Street Beach in South Boston with the ebb tide and need to reach Boston Light on Little Brewster Island before the tide turns again, some 5 to 6 hours later.

Weather: Anticipate ocean swells, wind, waves, and overcast skies. You may get glassy water or four-foot swells. This is New England; expect it all.

Swimmer notes: The swim starts from a sandy beach. Little Brewster has a pebble/rock beach. The water temperature is coldest at Little Brewster Island. You'll be in the open ocean for the duration of the swim, so expect to encounter some marine life.

Dates with favorable tides in 2026: TBD

The RBLS starts in the early morning at a specific time in the tide cycle to capitalize on that assistance, which means there are limited opportunities available each season.

Banner photo by Mina Elnaccash