When the Moon and Sun align with Earth—at new moon and full moon—their gravitational pulls reinforce each other. The result is spring tides, which have the greatest range between high and low water. Despite the name, spring tides occur throughout the year, roughly every two weeks.

High tides are higher and low tides are lower than average. Coastal flooding risks increase during spring tides, especially when they coincide with storms or strong onshore winds. Intertidal organisms experience the longest exposure and submergence times of the lunar month. The opposite phase, neap tides, occurs at quarter moons when the range is smallest.

Tide tables predict spring and neap cycles with precision. Local amplification by coastal geometry can make spring tidal ranges exceed ten meters in exceptional locations such as the Bay of Fundy. Mariners and coastal engineers schedule critical operations around the spring-neap cycle.

A spring tide can uncover intertidal zones that remain hidden during the rest of the month.