Seasons and sky
Slack Water
Direct answer
Slack Water is the brief interval when a tidal current speed is near its minimum before reversing or changing phase.
Slack Water is the low-current interval between flood and ebb flow.
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At a glance
- Found in
- Seasons & Earth Almanac
- Related
- Tidal Bore, Growing Degree Day, Astronomical Season, Equinox
Slack Water is the low-current interval between flood and ebb flow.
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The story behind Slack Water
Dedicated current observations showed that slack timing can differ substantially from vertical high and low water.
Why Slack Water matters
Slack Water can be important for diving, docking, bridge transit, and narrow-channel navigation.
Slack Water in practice: an example
In an inlet, high tide at a harbor gauge may occur before or after slack current in the channel.
Where readings of Slack Water go wrong
Slack Water is not guaranteed still water; wind, river discharge, eddies, and forecast error can leave dangerous flow.
Sources and editorial method
Research references used for this entry include:
- NOAA Tides and Currents Glossary - Operational definitions for tides, tidal currents, ranges, datums, bores, and amphidromic systems.
- Source
- The Great Almanac Dictionary
- Category
- Seasons & Earth Almanac
- Last updated
- 2026-09-26
Check the current-station slack time
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Common questions
What is slack water?
Slack Water is the brief interval when a tidal current speed is near its minimum before reversing or changing phase.
What do people get wrong about slack water?
Slack Water is not guaranteed still water; wind, river discharge, eddies, and forecast error can leave dangerous flow.
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