The five essentials
- Time: the predicted high or low at the listed station.
- Height: predicted water level relative to the named datum.
- Range: the height difference between a high and adjacent low.
- Station: the exact reference location.
- Stage: incoming, outgoing, or near a turn during your trip.
High and low times
The listed time marks a predicted water-level maximum or minimum at the station. It does not necessarily mark slack current, and it does not mean every nearby creek reaches the same level at the same minute. Distance, depth, channel shape, and friction create local lag.
Tide height and vertical datum
A tide height is measured relative to a reference plane called a vertical datum, such as Mean Lower Low Water. It is not simply “feet of water” at your fishing spot. Charted depth, local bottom elevation, waves, wind, and actual observed level are separate pieces. Always verify which datum a source uses before comparing numbers from two systems.
Tide range
Subtract the low height from the adjacent high height to estimate range. Larger ranges usually imply more water exchange and potentially faster flow through narrow features. The same range can behave differently in a deep channel, shallow flat, inlet, and marsh creek.
Reading the tide stage
Between a low and the next high, the water level is generally rising or incoming. Between a high and the next low, it is generally falling or outgoing. The change is curved rather than perfectly linear, so a simple “divide by six” estimate is only an approximation. Outgoing Tide’s hourly table helps visualize the curve, but the high and low predictions remain the official reference points.
Water level is not current
Tide refers to the rise and fall of water; tidal current is its horizontal movement. Current can continue after a predicted high or low, especially near an inlet or in a long estuary. Use current predictions where available and learn local timing before navigating shallow or fast water.
Predicted versus observed water
Astronomical predictions do not include every short-term weather effect. Sustained wind and atmospheric pressure can shift observed level above or below the table. Compare real-time water-level observations with predictions when a station provides them, particularly during strong weather.
Choosing the best station
Choose a nearby station connected to the same water body and understand whether it is a primary or subordinate station. The geographically closest station is not always the most representative if an inlet, barrier, river reach, or bay changes how water moves.
Primary references
Planning only: Do not use a recreational tide display as your sole source for navigation or under-keel clearance. Use current nautical products, official warnings, and direct observations.