During which phase might you observe the highest and lowest tides?

The observation of the highest and lowest tides occurs during spring tides. This phenomenon takes place when the gravitational forces of the moon and the sun align closely, which happens during the full moon and new moon phases. During this alignment, the combined gravitational pull results in more extreme tidal conditions, leading to notably higher high tides and lower low tides.

In contrast, neap tides, occurring when the moon is in its first or third quarter phase, present a lesser variation between high and low tides. Equinox tides, while they may result in increased tidal activity due to the sun's position, do not distinctly cause the highest and lowest tides like spring tides do. Constant tides is not a standard term used in tidal discussions, so it does not apply in this context. Therefore, spring tides are recognized as the time when tidal fluctuations are at their most extreme, which confirms why this option is correct.