Old Sow whirlpool

[1] The whirlpool is caused by local bathymetry and a 20-foot (6.1 m) tidal range[2] where waters exchange between Passamaquoddy Bay and the Bay of Fundy, combined with the topography of the location's sea floor at the confluence of the numerous local currents through channels and over small sea mounts.

Tremendous water turbulence occurs locally in the greater Old Sow area, but it does not usually constitute a navigation hazard for motorized vessels with experienced operators at the helm; however, small craft—especially vessels with keels (sailboats) and human-powered vessels—are warned to avoid these waters when the tide is running.

[5] Besides Old Sow and its numerous "piglets" (small and medium whirlpools surrounding Old Sow), other area phenomena include standing waves, upwellings (that on rare occasion may even spout several feet into the air), and 10–17 feet (3.0–5.2 m) deep or more, circular and trench-shaped depressions in the water.

The changes in local water flow from the dikes reportedly reduced predictability of the "funnel" effect of Old Sow.

[6] On March 28, 1830, a two-mast schooner was destroyed in the whirlpool drowning brothers Robert, James and William Stover whose widowed mother lived in Fairhaven.