Minus tides at Brier Island

What a minus tide is

Tide heights are measured from a datum — here Chart Datum — which is roughly the average of the lower low waters. Most low tides sit a little above it. A few times a year one falls below, and the height is printed as a negative number: a minus tide.

They happen on the same days as the king tides, and for the same reason. When the sun and moon pull together the water comes up further than usual, and it also goes out further than usual. The big high and the big low are six hours apart on the same day.

A foot below datum does not sound like much. On a shallow shore it can mean a few hundred yards of ground uncovered that nobody sees the rest of the year.

What to do at low water at Brier Island

A forty-foot tide uncovers an extraordinary amount of ground. At Burntcoat Head the sea floor is walkable at low water and under five storeys six hours later; the park times its openings to it. At Blomidon, Parrsboro and along the Minas shore the flats run out most of a mile.

Clam digging is the traditional use and the amethyst and fossil hunting at Parrsboro and Wasson Bluff work the same hours. Anything taken from the flats is regulated by Fisheries and Oceans Canada; check the current closures before harvesting.

Go out on a falling tide, know when it turns, and be back before it does. The water returns faster than anyone can walk, and it fills the channels behind you first.

Going out safely

The water comes back. Work out when the tide turns before you walk out to anything, and allow more time than the return trip took — a rising tide fills channels behind you before it reaches where you are standing.

Wet rock is slippery, and what is exposed at a minus tide has been underwater long enough to be covered in weed. Anything living out there is usually protected by state or local rules; look it up before taking any of it home.