What is described as slack water?

Slack water refers to the period during a tidal cycle when the tidal current is at or near its minimum speed, effectively coming to a stop before reversing direction. This occurs between the ebb tide and the flood tide, or vice versa. The significance of slack water is that vessel traffic can be safer and more manageable during this time, as currents do not exert a strong influence on navigation.

This option accurately captures the essence of slack water, as it specifically describes the condition when current velocities are so low that they approach zero. The other choices relate to different aspects of tidal phenomena, such as the peak height of a tide, the lowest point of a tidal current, and times of maximum tidal flow, but they do not represent the state where the current is exerting the least influence on navigational conditions. Therefore, acknowledging that slack water is directly tied to nearly stagnant currents clarifies its critical role in navigation and seamanship.