Old Sow Whirlpool

70 billion cubic feet of water enter Passamaquoddy Bay on the average incoming tide. (Passamaquoddy Bay includes the waters north, west, and south of Deer Island, west and north of Campobello Island, Cobscook Bay, and between West Quoddy Head and Campobello Island.)

The greatest predicted tide during normal weather at the Eastport tide sensing station — the closest station to Old Sow (about 1 mile away) — is a range (the difference between high tide and low tide) of over 26 feet. (The nearest Canadian tide sensing station is in Saint John, New Brunswick, Canada.)

The tide changes from low to high or from high to low in approximately six hours, in varying, but predictable, amounts. The following table shows the typical ratio of water that moves each hour as compared to the total volume of water that moves with any tide cycle (during periods of average weather).

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Thus, during the first hour of average movement from slack low water, approximately over 3.3 billion cubic feet of water move into Passamaquoddy Bay. During the second hour, over 6.6 billion cubic feet move in, and during the third hour, over 9.9 billion cubic feet enter the bay. Then, the volume of movement decreases in the same, but reverse order, until high slack water is reached. When the tide changes to low, it repeats the same pattern of hourly proportions.

Since the greatest volume of water moves during mid-tide, that's a great time to witness numerous small-to-medium gyres, standing waves, boils, and even possibly a rare spout. Old Sow and large troughs in the water, however, are apt to appear unexpectedly, during the period after mid-tide.

Greater whirlpool activity is experienced during spring tides.

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