The water this site is named for

What is slack water?

Slack water is the short stretch of time when a tidal current turns around. The flood, the current that carries the rising tide in, slows and stops, and the ebb, the current that carries the falling tide back out, begins. Or the other way round. For a while the water barely moves, and in a narrow pass that lull is when a boat can get through.

A window, not a moment

Slack is the time the stream is weak enough to work with

The current is exactly zero for an instant. What matters on the water is the time around that instant, while the stream is too weak to set you onto the rocks or stop you making way.

There is no single speed that counts as slack. Workable water depends on the boat: a kayak and a trawler don’t share a limit.

The common mistake

Slack is not high or low tide

It’s natural to assume the current stops at high and low tide. Along an open coast it roughly does. In a pass it often doesn’t: the stream there runs on the difference in water level between the two ends, and it turns when that difference does, not when the tide peaks on either side.

Deception Pass State Park has a tide gauge 0.6 nautical miles from Deception Pass (Narrows). On Monday, October 19, slack in the pass came at 10:47pm, 6 h 53 min before low water at the gauge.

The tide at Deception Pass State Park above the current in Deception Pass (Narrows). Slack at 10:47pm comes 6 h 53 min before low water at 5:40am.FloodEbbLow 4:42amHigh 1:59pmTide at Deception Pass State ParkCurrent in Deception Pass (Narrows)6 h 53 min6:00am12:00pm6:00pm
Monday, October 19, times local to the pass. Dashed lines are the gauge’s highs and lows; solid green lines are slack in the pass. The dotted green lines mark 1.5 knots either way, and the curve turns green while the current stays between them.

That day is not unusual. Over the 14 days from Monday, October 19, 22 of the 54 slacks in Deception Pass fall within half an hour of a high or low at the gauge. 23 are an hour or more from one, and the furthest is 7 h 8 min away.

A tide table read as a slack table gets a pass wrong. Current stations publish their own slack times, so use the current station for the water you are crossing.

Minutes or hours

How long slack lasts

It depends on the pass and on the size of the exchange. A narrow pass with a fast stream swings from flood to ebb with hardly a pause; a broad channel with a weaker stream can idle under the band for hours. These are the next 14 days at each station, counting slack as under 1.5 knots:

Even at one station the window moves with the tide’s range. At Deception Pass the shortest slack in that stretch, 54 min on Friday, October 23, sits between streams reaching 6.6 knots. The longest, 1 h 46 min on Monday, October 19, sits between streams reaching 4.2 knots. A bigger exchange means a faster stream and a shorter slack.

Planning a transit

When to go

Each turn has two slacks on a current table: slack before flood, as the ebb dies, and slack before ebb, as the flood dies. Pick the one that leaves the next stream running your way. Arrive as the opposing stream eases, go through at the turn, and the new stream carries you on rather than building against you.

Plan around the window, not the minute. Predictions are not observations: wind, river runoff and air pressure can move slack by minutes or more. Be at the entrance when the window opens, not when it peaks, and know where you will wait if the stream turns early.

Next

Where to find slack water

Look up the current station for the water you are crossing, not the nearest tide port. The Slackwater app predicts slack for current stations across the US and Canada.